I think you misunderstood. It does give you the full 60kW anytime it can, even at low speeds. The only time it doesn't is if it's physically impossible, like if you were only going 5mph and there's simply not 60kW of energy to recover. He said it doesn't give you whiplash, but it gives you full regen quite quickly. It's enough that it makes for awkward driving the first couple times you decal until you get used to it. It's much like driving a car that has much touchier brakes than you're used to. By the time you could move your foot to the brake, the MS is already giving you full regen. As others have said, it's much easier this way because you can easily get full regen anytime you want it without using the friction brakes at all. Even on my 2 test drives, I was already used to it enough that the only time I was using the brakes was for the last few mph pulling up to a stoplight (creep was turned on). I think you should go test drive one again and make sure regen is set in standard mode. It really sounds like yours was set in low, as you already hinted it may have been.
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The brake pedal
- Thread starter Donkasan
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I think you misunderstood. It does give you the full 60kW anytime it can, even at low speeds. The only time it doesn't is if it's physically impossible, like if you were only going 5mph and there's simply not 60kW of energy to recover. He said it doesn't give you whiplash, but it gives you full regen quite quickly. It's enough that it makes for awkward driving the first couple times you decal until you get used to it. It's much like driving a car that has much touchier brakes than you're used to. By the time you could move your foot to the brake, the MS is already giving you full regen. As others have said, it's much easier this way because you can easily get full regen anytime you want it without using the friction brakes at all. Even on my 2 test drives, I was already used to it enough that the only time I was using the brakes was for the last few mph pulling up to a stoplight (creep was turned on). I think you should go test drive one again and make sure regen is set in standard mode. It really sounds like yours was set in low, as you already hinted it may have been.
Depending on the situation, it may actually be true that locking up the fronts is more dangerous. If you are in winter conditions and you lock up the fronts, you will lose all steering control even though you may not be going very fast. Prior to the introduction of ABS brakes I know of a few people who crashed because of this - in the heat of the moment they forgot to pump the brakes.
Now if you are at the limit of grip at high speed, e.g. driving on a dry racetrack at high speed, then yes, losing the front will cause you to plow, and losing the rear will cause you to spin. The latter is way harder to control, especially if you're not experienced doing that kind of thing.
Another person explained it differently and that sounds correct:
VolkerP said:
08-07-2012, 03:38 AM
Regen is limited to 60kW power fed back into the 85kWh battery pack. We don't know if the smaller packs will have even less regen. The Roadster power gauge goes up to 40kW regenerated power. With Model S at nearly twice the Roadster's weight, there is twice the kinetic energy to deal with but only 50% more regen power. That will limit max regen deceleration to 2/3 of Roadster max regen deceleration.In addition to that, Tesla smoothed the curve when regen kicks in. In the Roadster, regen jumps to 100% as fast as you lift the foot off the accelerator pedal. Not so in Model S. There is a short delay during which regen is building up. I don't know the length of the delay. But a quarter of a second would be enough to make the transition feel much softer. That was Tesla's design intent and they succeeded.
from http://www.teslamotorsclub.com/showthread.php/9614-Performance-Regen-vs-85-kWh-Regen
Someone else also suggests that Tesla may have capped regen at -0.15g, rather than at some specific kW rating.
And it make senses from a driving experience perspective not to design in the full possible regen that the generator and battery are capable of by simply releasing the accel. That would be too abrupt -- too much like a golf cart or go kart. A gradual curve is better -- or even better a cap on the amount gs.
But if you ever want to decel more than the curve or cap allows, your only option is friction braking. It could be that the amount of energy there just isn't worth trying to capture. It is certainly true that if you are very efficient and lucky in not over accelerating then you rarely have to decel more than the accel pedal release will allow. But the point remains that there is by design forgone regen opportunity lost whenever you need more regen than allowed by the accel release.
Again to summarize, what are limiting factors in how much regen to capture? The factors include:
1) what the battery can take. The Superchargers can deliver 90kW? so presumably we aren't close to this limit of the battery.
2) What the motor/generator mode can deliver. It looks like this is capped at 60kW?
3) The braking force on the tires before they lock/lose traction. This is different for using the front only, or rear only, or all four wheels. Certainly you can capture the most force from using all four wheels, next most would be just the fronts. Last would be the rear wheels only.
4) From a driving experience there may be too much "regen surprise" so a limiting factor would be how much regen can the driver experience before they feel like they are in a go cart? Should the car come to a short halt when the driver releases the accel?
It looks like the MS is better than anyone else at dealing with 1 and 2. The electronics probably generate and receive more regen than any other cars.
But 3 and 4 are substantial limits on the amount of regen that is probably well below what would be possible up to the limits of 1 and 2. Other cars deals with 3 and 4 by allowing regen from the front wheels or from all wheels and allow control of the strongest regen from the brake pedal instead of only the accel pedal.
But again, it could be that the amount of energy above what is designed into the accel release curve just isn't worth the bother of trying to capture from inputs from the brake pedal. Certainly the more efficient of a driver you are (and less you need to slow down more -0.15gs or whatever the accel release allows) the less it matters. So while #4 is a limit, it doesn't have much a mileage effect.
And the awd Teslas will address #3.
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Momentary understeer has an easy recovery -- just ease up on the braking to allow the front wheels to rotate again. Imperfect and somewhat delayed ABS does this in enough time for understeer.
Momentary oversteer can send your rear spinning around from which there is no recovery. Imperfect and delayed ABS can be too slow and the car can still spin out. That is why stability control which will individually brake the wheels to correct the spining yaw movement is necessary to recover from oversteer situations but even that has its limits and cars with stability control can still oversteer into spinouts on high speed curves or where traction is limited.
I don't understand why you seem to think the brake pedal is needed for front wheel regenerative braking. The Prius is FWD, so the regenerative braking comes from the front wheels. They could do the same thing by just using the accelerator to control 100% of the regen force. The MS, on the other hand, is RWD, so the regenerative braking is dealt with by the rear wheels. Whether they mixed the regen into the brake or not is irrelevant to the amount of regenerative braking available. 60kW will be the max no matter what means you use to get there. Personally, I've not driven a Prius, but I'll defer to the people here who've said they have 100k+ miles of driving a Prius and lots of MS seat time as well and prefer the way Tesla handles it. I personally like that it's dead simple to find max regen on the MS and then be able to add brakes if that's not enough. Having to modulate the brakes to get the most regen possible doesn't seem like as good a solution.
I know I'm being a bit of a stickler here, but I wouldn't consider stability control to be necessary to correct oversteer any more than ABS is necessary in slippery conditions (I grew up driving older non-ABS cars in Minnesota). It's just easier for the average driver.
I know I'm being a bit of a stickler here, but I wouldn't consider stability control to be necessary to correct oversteer any more than ABS is necessary in slippery conditions (I grew up driving older non-ABS cars in Minnesota). It's just easier for the average driver.
It might be able to see this combining dashcam accelerometer data with REST data. Syncing up the two can sometimes be tricky, but I might try looking into this at some point.
A thorny issue is how to detect when it's purely regen vs. when I happen to touch the brakes because I don't think either data source (directly or indirectly) tells me when friction brakes are applied.
I didnt mean to suggest that the brake pedal is needed for front wheel regen. Rather I think the brake pedal is a reasonable driver input to cause additional and more forceful regen. Separately I think additional and more forceful regen is available from the front wheels rather than the rear wheels. And if you have the latter, you are more likely to find the former ueful. they are separate issues but both are implemented in the toyota hsd regen.
How do you know that you are getting "max regen" by merely releasing the accel?even at slower speeds? How do you know that the regen isnt capped by design at -0.15 gs so as to limit the regen surprise effect? And that the battery and motor could generate additional regen (even from the rear wheels before they locked up)?
A perfectly reasonable design could be to have a capped amount of regen available from releasing the accel, and additional regen available as needed by giving additional driver input. That input could be given, e.g., through application of the brake pedal.
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Coming from Honda's IMA implementation, I couldn't be happier with TM implementation on Model S as it is simple, very functional and it is so unbelievably smooth. Kinda like warm butter awesomeness.
Agree. I think the OP needs to drive the Model S a bit more and stop over-analyzing this. I had a Toyota Estima hybrid minivan in Tokyo from 2003-2010. While I liked the car and the regen, the brakes felt like going through mushy, weak braking before I got to the real brakes. With the S I control the bulk of my speed using the one pedal, only hitting the brakes at 5mph or so at intersections, or when I need to stop suddenly.
I find I drive more smoothly and economically using the one pedal, and when I need to stop urgently I much prefer knowing I have real, powerful brakes to rely on. They saved a skunk's life (and me an extensive detailing) earlier this summer.
In my experience Hybrid regen brakes from two generations of Prius and multiple models of Lexus hybrids all work perfectly. And in all cases there is virtually no brake dust and minimal brake pad wear.
I don't think anyone answered the question of whether the teslas regen is limited to a certain specified curve or negative g forces or if it is limited only by the ability of the battery to accept a charge.
I don't think anyone answered the question of whether the teslas regen is limited to a certain specified curve or negative g forces or if it is limited only by the ability of the battery to accept a charge.
Roadster has the same regen as the Model S. It's a lighter car so it has a stronger effect.
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As I understand it, on full pedal lift (max regen) both Teslas max out the amount of energy the battery can receive.
mnx
2018 M3P
Since a superchager can pump 90kW or even 120kW into the Model S, I would assume that the batteries could handle that level of regen, but people already complain that the regen is inconsistent (cold weather, range charge, traction control kicking out regen from a bump etc.) Having 120kW max regen would only exacerbate the issues with lack of regen.
It would also make regen less consistient. eg. 120kW regen available when the batteries are low, but only 60kW available when the batteries have a 90% SOC. You really want the car to be as consistent as possible.
Assuming real wheel traction wouldn't generally be an issue at the 90-120kW regen level (it certainly could be in winter, wet roads etc.) that is when blending even higher levels of regen on the brake pedal could be beneficial. Personally I like the system as is. It's not perfect, (going downhill @ 25mph the regen feels very ineffective for example) but I've heard too many complaints about the braking system/blend on hybrids. I'd rather have a consistent braking experience than save a kWh here and there by using the brakes slightly less.
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As with acceleration, there is a cap on both torque and on power.
At high speeds, you're limited to a 60 kW cap on power.
At low speeds, you're limited to a maximum amount of torque.
To me, the regeneration caps seem to be about 20% of my P85's acceleration caps.
e.g., on acceleration, my car switches from the torque limit to the power limit somewhere around 40 mph, and on deceleration, it seems that the green bar starts backing away from 60 kW somewhere in the 30s of mph.
I don't know the reason for the caps. I'm surprised that the caps are not higher for the P85 than for a 60 kW. and I suspect the caps were designed for the nonexistent 40 kW battery. Tesla might have the most regen of any manufacturer, but I'd still choose more.
Regarding how we know when the car is providing the maximum regen, well, the car shows the regenerated power on the screen. It's pretty easy to see that if you take your foot off of the go pedal on the freeway, you'll get 60 kW of regen within a fraction of a second. It's possible that the regen is smoothly ramped up over that fraction of a second, but compared with the time to get your foot onto the brake pedal, the smoothing is unimportant.
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Incidentally, I somewhat disagree with your statement that there is a maximum amount of deceleration that can be tolerated with no foot on either pedal. A lot of regen is awkward the first time you drive your car. but after your brain internalizes that no pedals = quick deceleration, I don't see what the problem would be.
[well, other than turning cruise control off. that's still something that's awkward. When I decide it's time I want the cruise control off, I spend about a second trying to get the right pressure on the go pedal, and during that second the cars in front of me are getting closer and closer. ACC would be helpful here...]
Like others, I appreciate that coming off of a highway, I can take my foot off of the pedals and know that I'm recapturing the most energy I can. With regen integrated into the brakes, it would seem harder to find the place where I'm getting maximum regen without any friction braking.
All the talk about whether the Model S could have more than 60kW regen is not meaningful. A lot more just isn't needed.
The regen is sufficient to capture most of the energy that is possible to capture in daily driving. If you are an idiot leadfoot who insists on charging hard up to a red light and hammering the brakes - then more regen could help you - but those people need to learn how to drive.
I wouldn't turn down a little bit more regen, but I don't find it at all necessary.
The regen is sufficient to capture most of the energy that is possible to capture in daily driving. If you are an idiot leadfoot who insists on charging hard up to a red light and hammering the brakes - then more regen could help you - but those people need to learn how to drive.
I wouldn't turn down a little bit more regen, but I don't find it at all necessary.
I don't charge hard up to a red light and hammer the brakes.
but I certainly use my brakes.
I'm not sure what "learn how to drive" means. I know how to drive with minimal use of the brake pedal. I choose not to.
On red lights, yeah, there's not much point to getting to the red light quickly.
Stop signs and corners, though, are a different matter.
Saying that more than 60 kW of regen is unnecessary is like saying that more than 100 kW of acceleration is unnecessary. It's more energy efficient to keep your acceleration below 100 kW, and you really don't need more than that in daily driving.
but I bought a P85, so I guess I'm an idiot leadfoot.
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Me 2, but not always. Would be cool to have a setting/higher re-gen though for track purposes.
Me 2, but not always. Would be cool to have a setting/higher re-gen though for track purposes.
I would be able to adapt to higher regen off track too. I love one pedal driving.
If you had unlimited regen at your disposal so that you could make even the most panic stop with all regen, then you could charge hard up to any stop and regain all the possible energy. But I bet that you are still getting the benefit of the regen and it is capturing a large portion of the available energy. I think most stops/slowdowns are lights and turns where you are constrained by other traffic and where the "coast to a stop" costs no more time than the "charge hard and jam on the brakes".
I also bet that unlimited regen might change the total energy captured by the average Tesla driver from 90% to 100% of theoretical max, and would be a fine thing to do if it was free and easy, but not worth it otherwise.
And I would characterize an "idiot leadfoot" as someone who charges hard and slams on the brakes when it can not possibly save them any time ( up to a red light that will not change any faster if you get there sooner ), but a "leadfoot" as someone who charges hard because they are actually saving time. I also have a P85 and trade efficiency for time when it suits me.
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