Regenerative Braking Behavior Poll

[Marc Weiss]

Hi all,

Just joined this forum as I await the invitation to configure my Model 3. I made my reservation on March 31, 2016. Meantime, I've been driving a leased BMW i3 since early 2016, so more than two years now.

The i3 regen brings the car to a full stop; I was surprised (and somewhat disappointed) when I recently drove a Model S and it didn't do the same.

I can say in reply to some of the concerns posted in this thread that I still use the brake when I need to stop quickly and I don't think my reaction time has slowed down at all. But one pedal driving is such a pleasure, particularly in city driving, that I really hope Tesla will offer that option to drivers who want it.

I would sign up for that on Day 1, as I did for the Model 3.

 

[jerry33]

Having the regen system bring the car to a complete stop wastes energy and means the friction brakes are more prone to rust. The current system is the best compromise.

 

[BerTX]

This poll needs an "I don't care" option...

 

[Helmuth]

Having the regen system bring the car to a complete stop wastes energy and means the friction brakes are more prone to rust. The current system is the best compromise.

You (rather the system) would need to use the friction brakes anyway to bring the car to a complete stop.
But it would be nice if the regen would use the regular brakes like it does while using TACC and AP...
I would love to have real one pedal driving!

 

[jerry33]

You (rather the system) would need to use the friction brakes anyway to bring the car to a complete stop.
But it would be nice if the regen would use the regular brakes like it does while using TACC and AP...
I would love to have real one pedal driving!

The issue with that is the additional amount of complexity required. A whole new set of mechanical pieces is needed to simulate pedal pushing. Toyota devotes several pages of diagrams in the New Car Features Manual to explain how they do it, and it still doesn't have one pedal driving. If it could be done simply, that would be different.

 

[jgs]

Early in my ownership I was convinced the ideal would be for the car to present a consistent behavior when regen was limited, by automatically filling in with friction brakes. Leaving aside the complexity issues @jerry33 mentions and assuming for sake of discussion (but not actually stipulated) that it’s even possible to deliver a satisfying user experience with a blended system like this, I’m still not convinced any more. As I’ve driven the car — and it really didn’t take very long — I’ve come to accommodate my driving style to the amount of regen available. My preference is to use regen in preference to friction brakes (and coasting in preference to regen but that’s another story) so when regen is limited, I allow longer stopping distances. If automatic systems filled in with friction brakes and always delivered the same stopping force when I eased off the pedal, I wouldn’t get the same kind of feedback that allows me to do this. I suppose I still could watch the regen meter (although I guess the Model 3 doesn’t have a very good regen meter?) but it’s not the same — right now I can’t engage the friction brakes by mistake, by simply lifting off the accelerator. I still can’t feather the accelerator perfectly to hover at zero, after three years of practice, but at least when I get it wrong I’m only slipping a little into the regen or acceleration side. In the imagined design, when I feathered the accelerator wrong, I’d be using the brakes.

On the balance, I no longer want blended braking even if it were possible to do right (which I doubt).

 

[maxpower2078]

As a prospective buyer I was wondering how this works. I have a hill on my commute to work and currently drive a plugin hybrid so no regen brakes but it does register some slight energy recouping whenever i have my foot off the pedal and not on the break but I still get the momentum of the hill.

With the use of regen, will I have to use the accelerator in order to maintain the speed limit down a hill like this for example?

 

[brkaus]

As a prospective buyer I was wondering how this works. I have a hill on my commute to work and currently drive a plugin hybrid so no regen brakes but it does register some slight energy recouping whenever i have my foot off the pedal and not on the break but I still get the momentum of the hill.

With the use of regen, will I have to use the accelerator in order to maintain the speed limit down a hill like this for example?

Yes, maintaining speed requires use of the "go" pedal.

 

[jgs]

With the use of regen, will I have to use the accelerator in order to maintain the speed limit down a hill like this for example?

Depends on specific circumstances (e.g. if your battery is cold so regen limited, and the hill quite steep, you might not have to), but by and large, yes.

I tend to use TACC for much of my in-town driving, which relieves me of the tedium [1] of maintaining speed on my own.

[1] Mild sarcasm.

 

[Chaserr]

That would be awesome!

But I don't think it technically is possible.

It absolutely is, regen braking is just turning wheel motion into generated energy - absolutely any motion can generate energy and nature opposes free energy with physical resistance. RC cars use this to come to a complete stop so they don't need friction brakes.

A software update would allow it on all of our cars.

 

[jerry33]

It absolutely is, regen braking is just turning wheel motion into generated energy - absolutely any motion can generate energy and nature opposes free energy with physical resistance. RC cars use this to come to a complete stop so they don't need friction brakes.

A software update would allow it on all of our cars.

At the cost of range and keeping your brake pads clean.

 

[RogerHScott]

Depends on specific circumstances (e.g. if your battery is cold so regen limited, and the hill quite steep, you might not have to), but by and large, yes.

I tend to use TACC for much of my in-town driving, which relieves me of the tedium [1] of maintaining speed on my own.

[1] Mild sarcasm.

I've always wondered: does TACC make the maximum possible use of regenerative braking for deceleration? For that matter, does it use it at all?

 

[jgs]

I've always wondered: does TACC make the maximum possible use of regenerative braking for deceleration? For that matter, does it use it at all?

It absolutely does use it, you can see that easily by watching the energy meter while TACC is decelerating. I wouldn't say it "makes the maximum possible use" the same way a human driver would -- I'll often begin deceleration before TACC starts to, in order to avoid use of friction brakes, so my manual use of regen is probably more maximal than TACC's would have been. But it does use it, I suspect just like a human driver it doesn't call on the friction brakes until and unless it needs to in order to get the amount of deceleration it's looking for.

 

[Big Toys]

Hi everybody

I am not sure if this is relevant to this thread but since the latest upgrade 10.4, my regenerative brakes are less responsive than before in lower speed. There is a relatively steep slope near my home which I have to use everyday to get to the main road. Before the latest update, when I was going downhill, without touching any of mythe 2 pedals, the car could build up speed up to 35 miles an hour using almost full regenerative brake and I could see the green indicator on the dashboard going close to -50. Since the latest software update, the car builds up speed very quickly and if I manually do not apply the brake, it can just build up speed to over 80 miles before getting to the bottom.

In highway and with high speed the regenerative brakes works fine and similar effect of before update but in speed lower than 40 miles an hour it is not as responsive as before. I used to control my car almost with one pedal only and I had to apply the brake very lightly and at speed below 5 or 7 miles before coming to standstill but now I have to use the brakes to slow down the car. I checked my setting to see if the setting was changed to low or standard and it was in standard setting.

Has anyone had such experience after the latest software update?

Is it possible that Tesla realised the high effectiveness of regenerative brakes means less tear and wear of brake pads and less need to change them so they changed the setting forcing us to use more brakes?

There are other changes to the car behaviour especially AP since the latest update but I will post my experience in other threads about them.

Thanks for sharing with me yout thoughts.

Kind regards

I don't know it this applies to you or what yo are asking, but I found out that regen braking will not happen if you charge to or close to 100%. Yes, it was very disconcerting to lift off the gas only to find the car not slowing as expected. Your energy dial will show yellow dashes at the 5:00 position to let you know that regen is off. It will *sorta* kick in again after about 10 miles so ya gotta be careful, and the dashes will decrease and disappear.

 

[Shadnic]

This may be slightly off the topic, but anyone know if setting regen breaking to "low" helps with highway driving at all? I generally get very efficient kw/mi numbers on the highway with standard regen, but I always wondered if it would be even better if I was able to coast more/longer and not having to accelerate as consistently after the regen slows me down. Has anyone tested?

 

[RogerHScott]

I don't know it this applies to you or what yo are asking, but I found out that regen braking will not happen if you charge to or close to 100%. Yes, it was very disconcerting to lift off the gas only to find the car not slowing as expected. Your energy dial will show yellow dashes at the 5:00 position to let you know that regen is off. It will *sorta* kick in again after about 10 miles so ya gotta be careful, and the dashes will decrease and disappear.

This has always struck me as a danger in people becoming too used to regenerative braking. It should be thought of as an optimization, not a fundamental aspect of the car's operation. Just as with AP you are still driving and still ultimately responsible for driving the car, you are ultimately responsible for braking. Experienced owners will probably not have much difficulty with this, but new owners, renters, and people borrowing someone's Tesla might be dangerously caught off guard.
Note also that cold weather can limit regeneration even when the battery is not fully charged, which can catch you by surprise any time (if you live in the right climate).

 

[Big Toys]

This has always struck me as a danger in people becoming too used to regenerative braking. It should be thought of as an optimization, not a fundamental aspect of the car's operation. Just as with AP you are still driving and still ultimately responsible for driving the car, you are ultimately responsible for braking. Experienced owners will probably not have much difficulty with this, but new owners, renters, and people borrowing someone's Tesla might be dangerously caught off guard.
Note also that cold weather can limit regeneration even when the battery is not fully charged, which can catch you by surprise any time (if you live in the right climate).

Yes, it is dangerous. It is very disconcerting as the car fails to slow as expected.

 

[aerodyne]

This may be slightly off the topic, but anyone know if setting regen breaking to "low" helps with highway driving at all? I generally get very efficient kw/mi numbers on the highway with standard regen, but I always wondered if it would be even better if I was able to coast more/longer and not having to accelerate as consistently after the regen slows me down. Has anyone tested?

If Regen on the older cars is only 85% efficient, then coasting vs Regen would be more efficient. Someone makes a Tesla Chip that claims to do that.

But what percentage of a drive does one use Regen? Probably less than 10%.

If it was much higher, say 50%, I would be using TACC anyway, the heck with efficiency.

 

[jgs]

If Regen on the older cars is only 85% efficient

I didn't really follow the overall point of your post, but to this specific thing, ISTR round-trip efficiency for regen on the S is something like 60%.

 

[aerodyne]

I didn't really follow the overall point of your post, but to this specific thing, ISTR round-trip efficiency for regen on the S is something like 60%.

My point was, if you are using regen a lot, then by avoiding it by using the low setting or the Tesla Chip, you might gain range. However, you would have to Regen a lot. 10% of the driving time would get you max 1.5% gain.

I do not know what ISTR is, nor what The 60% number came from, but 85% is a pretty good number I think.