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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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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

View attachment 1223

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.
I understand the losses when using regen or b mode but how can I tell when I am actuating the brakes and throwing away the kinetic energy and wearing the brakes? Also, this thing coasts forever and hard to find the sweet spot.
 

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I understand the losses when using regen or b mode but how can I tell when I am actuating the brakes and throwing away the kinetic energy and wearing the brakes? Also, this thing coasts forever and hard to find the sweet spot.
The little green bar thingy should tell you when you are getting regenerative as opposed to using friction brakes.

Dave
 

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The little green bar thingy should tell you when you are getting regenerative as opposed to using friction brakes.

Dave
I am not sure what you mean that the green bar can show the difference between regen and friction braking. To me the green bar only shows how much regen is being used. Unless one were to assume that only if the green bar was at max and you continued pushing the brake peddle further it would then be using friction brakes?
Unlike some other EVs, the transition from regen to friction is so smooth in the ID4 that I, for one, can not feel that transition.
 

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Unlike some other EVs, the transition from regen to friction is so smooth in the ID4 that I, for one, can not feel that transition.
As far as I know, the ID. 4 is built on the only platform that does this type of blended braking.

Other EVs give you friction brakes as soon as the brake pedal is pressed.
 

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Unless one were to assume that only if the green bar was at max and you continued pushing the brake peddle further it would then be using friction brakes?
Yes this is how you can tell when it goes past regen into friction brakes. It is an amazingly smooth transition.
 

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I understand the losses when using regen or b mode but how can I tell when I am actuating the brakes and throwing away the kinetic energy and wearing the brakes?
I understand the question and I don't know of a good way to know for sure when the friction brakes are being blended in during a braking event. The ID.4 has such smooth blending, I don't think it is easy to distinguish between friction and regen. I've actually looked into it a bit and started writing a computer model, but there were just too many unknowns to get a good answer. What I did see is that in general the amount of regen at high speeds is limited by the rate at which the traction battery can be charged. I can't find the post now, but I believe that @VW TECHNICIAN said the battery charging is limited to something like 150 kW during regen, which means that at highway speeds the friction brakes must be used a bit more in the blending mix.

One option you have is if you normally drive in D mode, you can temporarily switch into B mode using the selector as sort of a paddle. I've never seen any indication that friction brakes are blended in when you don't actually touch the brake peddle, so if B mode provides enough deceleration in the situation you can know that you for sure that you didn't create any brake dust.
 

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In B mode....regen is artificially controlled via battery BMS .... traction control module and motor inverter. If foot brake is not used. If foot brake is used modulation is applied with mechanical brakes depending on foot brake sensors that measures how far did you push foot brake, how quickly did you move from accelerator to foot brake, steering wheel angle and various other sensors responsible for traction. Algorithm is quite complex.
Coast and predictive navigation assist regen is more efficient than any regen modulated by foot pedal. Some of this functions are not available or not enabled for NA market ( like predictive regen).
B mode is not using mechanical friction brakes. Foot brakes will also integrate regen before blending start. Algorithm will depend on driver speed reactions from accelerator pedal to foot pedal...how fast or deep is pushing foot brake. Brake booster mechanism have sensor that measures travel of foot pedal.....pressure applied and etc.
 

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Anyone who is more interested you can search for Bosch it will give you more insight on how this system operates.
New version brake booster will incorporate IOT connections to the cloud. Early stages will be more oriented for Bosch future development and manufacturers to fine tune emergency braking systems. Data collection will be beneficial to many different types of businesses. How government policy makers will control this data harvesting it is to be seen.
 

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As far as I know, the ID. 4 is built on the only platform that does this type of blended braking.

Other EVs give you friction brakes as soon as the brake pedal is pressed.
clearly not true. my fiat 500e had friction brake kick in below 5mph and it was not a smooth transition in my car
 

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clearly not true. my fiat 500e had friction brake kick in below 5mph and it was not a smooth transition in my car
Explain how the Fiat system works?

Are you saying if you step on the Fist's brake pedal, it doesn't immediately engsge the friction brakes?
 

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Explain how the Fiat system works?

Are you saying if you step on the Fist's brake pedal, it doesn't immediately engsge the friction brakes?
the fiat drive drain was also from bosch.
let's say i brake at 30mph then i see the regen power going in to the battery and feel the brake. then when slowed down to <5mph there was a little jerk and mechanical kicks in.
remember also based on physics regen theoretically can never get you to a zero stop because the regen (BEMF) is proportional to the velocity. so at lower velocities mechanical is needed to give reasonable braking
 

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I am not sure what you mean that the green bar can show the difference between regen and friction braking. To me the green bar only shows how much regen is being used. Unless one were to assume that only if the green bar was at max and you continued pushing the brake peddle further it would then be using friction brakes?
Unlike some other EVs, the transition from regen to friction is so smooth in the ID4 that I, for one, can not feel that transition.
Same for me. If VW just had a light that would come on when the brakes engage.
 

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the fiat drive drain was also from bosch.
let's say i brake at 30mph then i see the regen power going in to the battery and feel the brake. then when slowed down to <5mph there was a little jerk and mechanical kicks in.
remember also based on physics regen theoretically can never get you to a zero stop because the regen (BEMF) is proportional to the velocity. so at lower velocities mechanical is needed to give reasonable braking
Ah I stand corrected, although having difficulty finding a satisfactory description of how the Fiat system works. I find references to 8 mph but surely it's more complex than that, as marketing descriptions also say speed and force dependent.
 

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How about this thought. Is it possible to coast in B mode as well as it does in D mode? In other words, is there any amount of space, while in B mode, between regen (lifting your foot) and power (pushing your foot)? Or does it immediately go from regen to power and vice-versa? This would take a certain amount of finesse (practice) to do this if even possible.
 

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How about this thought. Is it possible to coast in B mode as well as it does in D mode? In other words, is there any amount of space, while in B mode, between regen (lifting your foot) and power (pushing your foot)? Or does it immediately go from regen to power and vice-versa? This would take a certain amount of finesse (practice) to do this if even possible.
Yes, but to me it's like flying the needle, and requires a bunch of heads-down time to watch for any deviation. Not safe nor enjoyable. I don't believe it can effectively be "seat of the pantsed." May as well either drop it into D (that's what it's for) or fire up your friendly autopilot.

BTW has anybody noticed if ACC behaves differently in D vs. B with respect to regen? I haven't spotted a difference.
 

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BTW has anybody noticed if ACC behaves differently in D vs. B with respect to regen? I haven't spotted a difference.
From my experience in the ID.4 and the e-Golf (which functions similarly), ACC is a separate beast and doesn’t act any differently based on the mode you were in when you switched it on.
 
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After reading the regen article i played more with D mode , usually i use B mode.
It seems in D on a leveled road the car never comes to a stop, almost. It is similar to the N mode. I think the car clear so long due to it's weight, kinetic energy.
From an electric point of view i would agree that coasting is good. Basically the lower the current in the drive drain the less joules energy dissipation we have. Remember the loss goes with current square.
I like the B mode because it gives my nice speed control with gentle braking
 
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