Regen discourages coming to a full stop

[bradhs]

+1 ... Would be great to have a more aggressive regen, especially near coming to a stop. My ActiveE feel like it has stronger regen, and it also comes to a complete stop my quicker.

 

[FairFrank]

Based on my driving practice, I sympathize with those who plead for 1) a third, more powerfull - sportier - regen and 2) a HillStop/Anti-Roll-Back solution.
Of which the last 'wish' is the most importantfor people in driving areas with a lot of up hill stops.
When nearing an uphill parking ticket barrier, I use the manual brake for a full stop. When the barrier lifts, I switch quickly from manual brake to accellerator. However, the car still rolls back a little. Even with creep On.
Ok, ok, I have to practice more... but a little help from techtronics would be great.

 

[ecarfan]

I regularly drive the steep hills of San Francisco city. When stopped on hills I am able to use my left foot for the brake and right for the "go" pedal and I may drop back a few inches when starting from a dead stop, but that is not a problem. While a "hill hold" feature would certainly be convenient I don't consider it an essential feature (and I have such a feature in my Porsche Cayman and. Mini Cooper I used to own so I am very familiar with it). I am sure that in the future it could be implemented in the Model S through a future OTA update.

 

[AudubonB]

I use a double-foot technique as well. This is a very moderately technical exercise, but less so than rubbing your tummy at the same time as patting your head. I definitely recommend that those of you living in hilly terrain like San Francisco should learn it though....and am moderately perplexed you not be familiar with it.

Anyone who regularly drives/drove a manny tranny would have know of this, or at least if your car hadn't a hand-pull emergency brake.

The amusing caveat to this is that if and when you DO use both feet....and both pedals....a dashboard warning comes on letting you know you've two pedals pressed simultaneously. But it doesn't dock you any points.

 

[wycolo]

> Would be great to have a more aggressive regen, especially near coming to a stop. [bradhs]

Keep in mind that doing so on ice or packed snow might create problems. And don't forget that TC is always trying to function.


> you've two pedals pressed simultaneously. [AudubonB]

I've advocated 2-foot driving forever. I get the chimes as a reminder I'm doing this. How did you disable your chimes?
--

 

[ljwobker]

I'm not sure this quite explains it. Suppose you want to use regen to decelerate at a constant rate. The kinetic energy of the car at 5mph is only 1% of what it is at 50mph, but the required "regen" (in kW) at 5mph is also 1% of what it is at 50mph, so they should balance out. In my experience the regen applies a roughly constant deceleration (perhaps 0.1g) down to about 5mph, then tapers off below that. This is probably a comfort issue; the sudden stop at 0mph might feel rather abrupt if there were no tapering.

In any case, if regen is consistently applied from 50mph down to 5mph, that means the regen is capturing 99% of the available kinetic energy. (with ~30% losses converting to electricity of course.) The benefit of regenerating the last 5mph is negligible. But I'd still be curious to hear Tesla's official answer/reasoning about this.

This is almost certainly a design choice. Tesla *could* have chosen to keep the regen "on" all the way to a stop, but as others have noted there is virtually zero energy left to recover at these low speeds, so there's very little reason to do so. I'd wager that even once you're down around 10-15mph the energy being recovered isn't much more than a rounding error - it's much more about a consistent "feel" for the driver. There's also certainly some kind of clutch that engages/disengages the regen, and again I'm pretty certain that the decision on where to (dis)engage this as the car slows down was made far more with comfort/feel in mind than recovering that last bit of energy.

On the physics topic, the key ingredient being missed here is the frictional losses (tire resistance primarily) -- once you get very slow the proportion of energy being lost to friction is a lot higher.

 

[FairFrank]

Firmware tOS 5.9 now has Hill Start Support!