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Dangers of rapid regenerative braking?
- Thread starter chuckb
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- Driving Dynamics Model S
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Skotty
2014 S P85 | 2023 F-150L
I personally feel that regen on brake pedal offers a better driving experience, but only marginally and at the expense of several other cons.
Regen on brake pros:
1) Slightly better driving experience (subjective)
2) More familiar to newcomers
Regen on brake cons:
1) Much greater complexity (significant design issue)
2) No clear indication of when friction brakes begin to engage (significant usage issue)
I took a Tesla test drive, and they seemed almost obsessed with warning me about the regen, even knowing that I drive a Volt that can do the same thing (Volt will regen on accelerator when drive set to L). So they seem to prepare people for it pretty rigorously.
Regen on brake pros:
1) Slightly better driving experience (subjective)
2) More familiar to newcomers
Regen on brake cons:
1) Much greater complexity (significant design issue)
2) No clear indication of when friction brakes begin to engage (significant usage issue)
I took a Tesla test drive, and they seemed almost obsessed with warning me about the regen, even knowing that I drive a Volt that can do the same thing (Volt will regen on accelerator when drive set to L). So they seem to prepare people for it pretty rigorously.
mknox
Well-Known Member
One thing I've wondered about when I'm being tailgated down the freeway is the fact that if I have to jump off the accelerator quickly to brake, I'll start slowing quicker than the guy behind me. That is because the car starts to slow as soon as my foot comes off the accelerator whereas the guy behind won't start slowing until his foot comes off and moves over and applies the brake. Having said that, I haven't had any problems with being rear-ended and such.
I do agree that is very subjective.
Personally, I always preferred driving our Volt in "L" as it gave me a much better driving experience.
As for the score or so of MS owners I meet with monthly, I don't know of a single one that doesn't use the "Standard" setting for regen in their MS.
Skotty
2014 S P85 | 2023 F-150L
Even if I didn't like the regen on accelerator, I would still use it in a Tesla. Since Tesla doesn't integrate regen in the brake pedal at all, switching off of the standard setting would mean losing most of the regen ability. I prefer "automatic cruise" (coast) over "automatic brake" (regen on accelerator), but I wouldn't give up regen for it.
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It's not even remotely abrupt compared to a muscle car downshifting. I regularly locked up my rear tires downshifting 3rd->1st and letting out the clutch fairly quickly in my old 1979 Trans Am.
And the brake lights do come on with regenerative braking if it's decelerating quickly enough.
If someone rear ended you because of regenerative braking, they've no excuse except for being poor drivers.
Actually, that's a great observation in favor of aggressive regen braking. In a normal car, if you have to brake suddenly, braking doesn't begin until your foot hits the brake pedal. But with aggressive regen, braking begins the moment your foot starts to rise off the accelerator. That's probably something like 1/4 second faster, which could easily be enough to avoid an accident, or reduce its severity, or survive it.
mknox
Well-Known Member
Indeed. However, one of my early worries before I received the car was that this behavior in slippery winter conditions might lead to a loss to traction. Last winter was pretty brutal and I found the car to be just fine, so all things considered, the re-gen level seems to tuned just about right.
ToddRLockwood
Active Member
Regen without the brake pedal has two major advantages:
• All of the car's forward momentum is turned into electricity; none is lost to heat generated by the brakes.
• The brake pads will last many times longer. Tesla estimates 100K miles or more on a set of pads/rotors.
Personally, I much prefer Tesla's approach. There's a seamless transition from acceleration to deceleration. Since you get immediate braking when you let off the pedal, the Model S is inherently safer in traffic. And a lot less stressful too!
IMO strong regen braking only through the accelerator pedal offers a vastly improved driving experience because most of the time you use just one pedal instead of two. I got used to it in minutes (i.e. in less than an hour) and now it is the only way I want to drive!
I see no compelling reason for regen braking when using the brake pedal. It should only occur when backing off on the "go" pedal. That pedal becomes the primary speed modulator. It makes driving simple.
I would like to see the Model S have even stronger regen braking than it does know, such that on a level surface one could come to a full stop in a normal distance simply be lifting your foot completely off the go pedal. Right now it takes a long time to come to a full stop with your foot off the pedal.
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Not to pile on, but I'm with the rest of the folks that much prefer it on the accelerator.
Regen is very intuitive to me the way it is. I press the pedal to go faster, let up to go slower. Feels like the way it should behave. The brake is really only for unexpected situations and complete stops.
I don't buy this either. Every time you brake while going over a road irregularity the regen switches off and there is a transition where you have to modulate the brake pedal. In some cases it was so bad that cars were recalled. The "more familiar" doesn't seem right either as no one who drives a traditional car is used to the transition when regen stops. All the regen on the accelerator is way better.
You have the regen paddles. A regular Smart ED, has some regen on pedal lift but little in comparison to the Volt in L or the Tesla.
Unless they've changed the behavior in a recent update, the brake lights don't come on until > 30kW regen. I know this bc I've tested it extensively as people on the NJT were getting angry that I was "brake checking" them all the time and it was increasing the aggressive road rage behavior of the people behind me. It is because of this that I exclusively drive in low regen mode whenever I am on the highway as it limits regen to max 30kW and this will *not* engage the brake lights.
Or you could have trained yourself to avoid lifting your foot too quickly and uselessly brake checking people at freeway speeds. Unless the person in front of you has his brake lights on there is no reason to ever go above 30kWh of regen on the freeway (and have your own brake lights go on). On the other hand, if the person in front of you brakes it's nice not to waste energy slowing down by using friction brakes, which is what you need to do with regen set to low.
ThosEM
Space Weatherman
My experience with regen pre-Tesla was with a Lexus RX400h which I suppose to be similar to a Prius, but with more ICE power. The regen is via a combination of the accelerator and the brake pedal, trying I suppose to replicate the ICE experience as closely as possible. The gearshift has a D and a B setting, the B setting giving enchanced regen upon releasing the accelerator, similar to being in a lower gear ratio with an ICE. It also disables the cruise control, which is unfortunate, since it otherwise has no authority to slow the car on downhill stretches.
But the worst is stepping on the brake pedal. The transition from regenerative braking to normal brakes is so mushy and vague as to be beyond belief. One does get accustomed to it eventually, but my firm take-away from this experience is that these two functions are sufficiently distinct that they should not be mixed into one brake pedal.
I gather that the Cadillac ELR has a different setup with steering wheel flippers to control the regen level, and the Merc. B Class EV has some other scheme, and probably the i3 has yet another setup. Clearly there is not yet any standardization of this part of the user interface, but my preference so far is very much for the Model S scheme based on the Toyota/Lexus comparison.
Last winter I did find that Model S standard regen was sufficient to break loose the rear wheels on snow, when the accelerator was suddenly released as tends to happen when something unexpected occurs. That could be disconcerting when cornering, but is easily defeated by resuming some pedal pressure, and hence readily accommodated. It could be that low regen may be useful in such low traction situations. And of course the two wheel nature of regen means that the rear wheels have a greater wear rate than they would otherwise. The Model X will presumably avoid these issues by having four wheel drive and braking.
But the worst is stepping on the brake pedal. The transition from regenerative braking to normal brakes is so mushy and vague as to be beyond belief. One does get accustomed to it eventually, but my firm take-away from this experience is that these two functions are sufficiently distinct that they should not be mixed into one brake pedal.
I gather that the Cadillac ELR has a different setup with steering wheel flippers to control the regen level, and the Merc. B Class EV has some other scheme, and probably the i3 has yet another setup. Clearly there is not yet any standardization of this part of the user interface, but my preference so far is very much for the Model S scheme based on the Toyota/Lexus comparison.
Last winter I did find that Model S standard regen was sufficient to break loose the rear wheels on snow, when the accelerator was suddenly released as tends to happen when something unexpected occurs. That could be disconcerting when cornering, but is easily defeated by resuming some pedal pressure, and hence readily accommodated. It could be that low regen may be useful in such low traction situations. And of course the two wheel nature of regen means that the rear wheels have a greater wear rate than they would otherwise. The Model X will presumably avoid these issues by having four wheel drive and braking.
Seven7
Member
This is probably the fault of the person that works for Tesla not being able to read what type of customer they are taking for a test drive, or at least explaining the re-gen braking before they started the test drive.
If you are trying to sell a 70 to 120k car, you should listen to the potential buyer and if you hear that they don't know anything about re-gen braking then you had darn well better explain it to them, tell the buyer that the brake lights will come on without having to touch the brake pedal, tell them that the car will slow more than a common ICE car when they let off the accelerator, explain why this happens and the benefits of re-gen and also make sure they know re-gen can be switched off.
And do all that without making the buyer uneasy (-:
Just my .02
the P85 is so powerful that it's pedal is so touchy and sensitive I find this extremely difficult to do. Even the slightest let up of the pedal pulls back pretty hard at full regen and turns the brake lights on.
or you could just not tailgate the guy in front of you and give yourself enough room. better hypermiling this way unless you're trying to catch the draft of an 18 wheeler.
Agreed. It is possible, but you really have to pay attention. On anything other than perfectly flat roads, your energy consumption can easily swing from +60kW to -30kW (i.e. regen) with no change in speed. If not for the display, you wouldn't even know it's happening. It's shocking how a tiny change in gradient can translate into 100,000 watts difference in power. Of course, the fact that a watermelon-sized motor can absorb over 300,000 watts of electric power without melting is equally staggering.
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