[dallascajun]

One of the functions that I've paid attention to with my e-tron is the Brake Regen. I was under the assumption that aggressive regen is more efficient than coasting, so I setup my car for Manual Regen, and always double-pull the left paddle to get Max Regen. BUT, watching a review of the Taycan I heard a comment that the Porsche team believes that coasting is far more efficient than Brake Regen, therefore the Taycan was build very much like the e-tron in that it does NOT have a one-pedal functionality such as some of the other EVs in market.

I assume this is VERY dependent on driving style and/or whether driving on city/highway conditions. Without Regen, I can see the efficiency if you lift early and coast to a stop. I have noticed with max regen, I tend to lift early (as I'm conditioned with an ICE vehicle), but always end up pressing the accelerator again to reach my stopping point. This means I'm probably on the accelerator longer with max regen than if I was coasting.

The funny thing is my driving style is certainly more 'aggressive' than efficient, but questioning whether I set the regen back to Automatic (or Manual with minimal regen), or continue my current behavior of always setting to max regen when I get driving.

And I won't get started on the car going back to previous Regen setting when coming off of Cruise Control....

Thoughts?

 

[ioannisk]

Regen is regen

Regen is regen. The only difference between what you call "coasting" and what you call "regen" is the rate at which kinetic energy (from the car's speed) is converted to electrical energy (i.e., battery charge) by the electric motor (which, actually, in this case acts as a generator, not a motor). One-pedal functionality allows the driver to use the brake pedal ONLY for using the hydraulic brakes. This is a technically superior way of setting up an electric vehicle. Unfortunately, many drivers find it "weird", and end up complaining, because they are unwilling to change their driving habits: they are looking for the same behavior as an ICE vehicle, which is clearly suboptimal.

As for the question of efficiency, it depends on how you define efficiency. Yes, low-rate regen (for example, simply coasting) is, strictly speaking, more efficient because of two factors:

1. The electric generator spins slower, and therefore there are fewer thermal losses;

2. If you plan your stops sooner and end up coasting longer, you are using the accelerator pedal less.

This is the style of driving that is often exhibited by Prius drivers, who tend to slow down long before they have to come to a full stop, holding up everyone behind them.

If, on the other hand, you are want to use reasonable stopping distances, then the max regen with the double-tapping of the left paddle is better, because then you are less likely to have to use the hydraulic brakes at the end, and therefore more kinetic energy will be converted to battery charge.

 

[dallascajun]

Thanks for the perspective. While I'm not trying to hyper-mile my vehicle, I did notice that when I lift off the throttle (no regen), the thing coasts almost like there's no drag...it simply doesn't slow down as aggressively as an ICE vehicle, assuming since it doesn't have all of the mechanical 'drag' to deal with. I've been trying with both and can't seem to figure out what Regen setting I prefer: Auto or Manual (set to max), or what provides better efficiency.

 

[LegGodt]

Still confused. I thought the whole point of Audi’s implementation of regen is that when you apply the brake it mostly still chooses regen. The only difference with the one pedal driving is that you as a driver have to ‘tell’ the car you want to brake instead of coasting by pressing in the brake pedal.

My question is: what is most efficient way of getting regen for the etron? Through the auto application when the brake pedal is applied and the regen is used (so NOT the hydraulic brake) or by setting to manual and choosing level 1 or 2?

 

[GMTRB5]

It’s the same isn’t it? When braking as long as you’re under a certain force of braking it’s exactly the same as pulling the paddle shift on the steering wheel...?

 

[LegGodt]

I would have thought so too. Still I read about people convinced that manually setting to level 2 with the paddle shift gets more regen than simply using auto with the brake pedal.

 

[Joe]

It’s the same isn’t it? When braking as long as you’re under a certain force of braking it’s exactly the same as pulling the paddle shift on the steering wheel...?

Yes, as long as you keep the throttle bar in the green section of "braking" in the virtual cockpit the mechanical discs are not utilized. According to Audi this corresponds to about 0.3g of braking force. If you're driving conservatively and trying to any extent to be efficient, you will very rarely use the mechanical brakes. The paddle-shifter regen level is merely driver preference for how they would like the car to behave when they lift off the accelerator.

The mechanical brakes will periodically engage very slightly (completely imperceptibly to vehicle occupants) to wipe the braking surface clean. This occurs more often in the rain, I assume connected somehow to the windshield wiper usage.

 

[GMTRB5]

Nice - agree on the driving style - definitely makes you try and avoid the mechanical brakes kicking in..!

 

[JNealCox]

The Second Law of Thermodynamics always applies. Coasting will always be more efficient than regen.

 

[biff2bart]

Jnealcox is absolutely correct.

Practically speaking, to maximize range, consider these in priority (based on a "unit" of energy).

1. The vehicle's overall efficiency: this is the amount of energy required to move the vehicle a specific distance. It's a matter of: elevation gain (storing potential energy), friction, weight and the vehicle's internal electrical efficiency. Above certain speeds, the vehicle's aerodynamics will play a large part as well (though this is really part of friction). The E-tron isn't particularly good in this regard.
2. Coasting: coasting effectively let's you maximize #1 above in specific situations where you don't have to brake. You want to go the furthest possible distance for a given amount of energy spent. The E-tron is very good in this regard.
3. Braking. We're going to assume only regen braking. Any time you slow the vehicle down, you are converting kinetic energy into another kind of energy: if you use the friction brakes, that recovered energy is 100% heat. If you use regen braking that energy is about 85% recovered electrical energy into your battery and 15% heat. Then you have to spend that energy again (perhaps again at 85% efficiency) which makes for 0.85 x 0.85 = 72% net return on your regen braking.

Hence why coasting is overall better...

Now sometimes you can't coast (stop and go traffic) or your speed gets too high for a given situation. Then regen is better in every way then wasting kinetic / potential energy by turning it into heat.

For what the E-tron is, I think Audi's philosophy on coasting and regen is bang on.

 

[tylerdurden]

The Second Law of Thermodynamics always applies. Coasting will always be more efficient than regen.

This is the critical thing to understand. Energy in your battery is converted to forward momentum of your vehicle. There is some energy loss. Doing anything with that "momentum energy" such as bringing it back into the battery (aka Regen) is associated with further energy loss that would otherwise have remained giving you forward momentum.

The problem is that there are other cars/junctions etc. So you physically have to slow down to drive safely. So in this situation Regen is superior to "brake pedal" as with the latter all energy is converted to friction/heat in your pads/discs. Whereas with Regen some is used to recharge the battery.

On long motorway/highway drives I only tend to Regen on downhill stretches where there is gravity giving genuine free energy.

 

[JNealCox]

tylerburden, that is pretty much what I also do. On long downhill stretches I will Coast up to the speed I want and then pretty much use only the paddle shifters to adjust my speed, unless the slope gets too steep.