Todd Burch
14-Year Member
The regen case doesn't apply for the Model S, since all regen is tied to the throttle (the correct approach IMHO).
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P85D - Electric Mechanical Braking System
- Thread starter drewfabrics
- Start date
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- Driving Dynamics Model S
Hopefully with the Model D they can capture more brsking force and thus regen than would be desirable to trigger with only the throttle. That is it wouldn't be desirable for the car to come to a screeching halt when lifting off the accel pedal. That additional regen braking force is better triggered by the brake pedal.
green1
Active Member
Considering that we've established that the battery, and not the motor or the wheels, is the limiting factor, and that the battery pack on the D is unlikely to be able to accept charge at any faster rate than the non-D. What makes you come to this conclusion?
-- updated --
Just want to appologize if the tone here was too harsh, it appears that although I touched on this near the start of the thread, most of the discussion about this was in a different thread, not this one. My confusion between threads led me to think the poster should have read something that they probably have not seen.
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green1
Active Member
Superchargers only charge the car at 120kW. the other 10kW is to improve rates for a second car on the same charger.
Superchargers only charge at the 120kW rate when the battery is near empty, by half full the charge has tapered down to about 60kW, and by 3/4 full the charge is down to about 20kW or so. So the 60kW regen is already MORE than a supercharger anywhere above half charge on the battery.
If you did allow 120kW regen, you'd only have it for the bottom 10-20% of the battery, which means that your regen would be unpredictable, you'd never know how much braking force you get when you initiate regen, that's a very poor driving experience.
That is true - but with the nifty new EMBS you could also apply more regen with the brake pedal and get the best of both worlds while blending regen and friction brakes seamlessly.
green1
Active Member
The question is, can you really do "seamless", and is it worth the increased complexity for the very small gain (only providing a gain at very low states of charge)
On the flipside, if you are down to 10% range, you might be willing to trade a somewhat less seamless experience in order to maybe get a couple more miles to a charging station?
green1
Active Member
At that point you're best to avoid any changes in speed that you possibly can to maximize efficiency (coast as much as possible, limit braking and acceleration)
I did mention in one of my posts that moving the hightened part (above 60kW) to the brake pedal and making up the difference with the mechanical brakes was a possible option, but it's far from "simple" and it's a lot more effort than simply equating a second motor to more re-gen capability (plus, I suspect the single motor could handle the excess if it was desirable, it's a battery constraint)
On a somewhat related tangent, I also saw somewhere a suggestion that when regen is limited by a cold pack that the recovered power should be dumped in to the pack heater instead of regen being completely disabled. It's another innovative way of reducing brake use, and reducing energy consumption.
The reason that superchargers charge at the 120kW rate only when the battery is empty is because of the heat build-up in the battery. It is integral process, i.e. the time that battery is accepting the 120kW charge is as important as the charge level (120kW). The heat is proportional to the time and the average charging rate.
IMO, because heat profile of the battery before the regen braking is not equivalent to the heat profile of the battery after it has been charged at 120kW for 10 or so minutes, your conclusion that tapering of the supercharger rate below 120kW necessarily means that the 120kW of regen can't be used is not correct. The total heat dumped into the battery after 10 minutes of charging it at 120kW is clearly much higher than any reasonable driving scenario, prior to regen braking, except may be for a car competing on a race track.
I believe that the original limitation of 60kW regen on the rear axle was most likely limited by the considerations of the vehicle stability, not by maximum rate of charge that the battery can accept.
I believe that D models will have maximum regen at least doubled as compared to the rear drive versions. The 120kW will be automatically and dynamically distributed between the front and rear axle in a way that maintains stability of the vehicle
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green1
Active Member
Interesting theory. I don't buy it for a second, but it's interesting. I'd love to be proven wrong, however I highly doubt we'll see the D variants having double the regen of the normal ones.
EarlyAdopter
Active Member
My money is on double regen, half on lifting on the accelerator same as today, the other half on first engagement of the brake pedal. It's what the iBooster system was designed for. We'll see come December!
Todd Burch
14-Year Member
Why are people pushing for regen to be moved to the brakes? Keeping regen on the accelerator pedal is, IMHO, one of the best "driving feeling" decisions Tesla's made. Not just because it avoids the complexity of trying to keep natural braking feel, but because it lets you control the car in most driving situations without moving your foot very much.
mspohr
Well-Known Member
I guess we are all used to ICE cars where you have one pedal to go and another one to stop.
It really does make more sense to have a single pedal to control stopping and starting.
I've driven hydraulic snowcats where there is a single control for forward, reverse and turning... it's really quite easy to use.
It really does make more sense to have a single pedal to control stopping and starting.
I've driven hydraulic snowcats where there is a single control for forward, reverse and turning... it's really quite easy to use.
Cottonwood
Roadster#433, Model S#S37
I like to tell people who know how to drive a standard transmission, that the accelerator is like always driving in 2nd gear. They get it immediately.
If more regen were available, I would like a sport mode that was like always driving in 1st gear better than the hybrid brake pedal.
lolachampcar
Well-Known Member
ra-san
Member
I wrote a lengthy response to
but in the time I took, the thread moved on and perhaps ironically green1 ended up saying most of the bottom line of what I was thinking, except more concisely and in a few followup posts.
…then the thread moved on again and made me feel like throwing this out there anyway :tongue:
original post:
I'd always thought Regen amount was limited by power allowed into the pack once you got past a certain speed but after talking to engineers at the D event I'm not as sure it's as limited as I thought. It sounded to me like they have increased the amount of power you can draw from the pack, at least for short bursts if not sustained. If they allow more pulled out, why not more in? Also I don't think the pack itself is the limit due to Supercharger rates, and you can see from the rates dumped to the motor on hard accel that the motor itself can use (and therefore generate?) substantially more than what we see as the current regen limit.
So, I'm more inclined to believe the current limit is based on handling effects and the desire to not surprise the crowd used to automatic transmissions in a large sedan (though would argue that the latter should be driven by user preference). Supporting the handling effects influencing current limits is that the drive train engineer spoke of more regen being available due to the two motors allowing more regen before handling was affected, and that there was a limit of how much regen could be allowed from foot off accelerator due to stability. Admittedly he did not specifically indicate that was a limit they were already hitting, but he did talk about a pet idea of his being an additional controller allowing one to manually add extra regen after foot off accelerator (like a handbrake or additional foot control). If a drivetrain engineer was mentioning this and thinking about how to do it in the context of the S rather than just an interesting idea for electric in general, it indicates to me that there may be more regen potential than what there is access to right now via the accelerator pedal. This is conjecture, but I have submitted questions to find out details. We'll see if they are answered.
Warning: wall of text thoughts to follow: tl;dr conclusion, give us as much more regen tied to accel pedal as we can safely handle as a preference setting. Assuming that's more than current, I doubt it's worth the complexity/cost/potential for failure of feel to integrate with the brake pedal.
Here's my thinking behind that though:
So if there is more regen avail, how best to access it, or should it be...
I originally thought the accel pedal was the best way to handle it, but that was when I thought there wasn't more, or at least much more, avail and that all available could be accessed without unsafe conditions being created by your foot suddenly letting off the pedal.
*If* there is more avail in excess of what could be safely put on the accel pedal (and adjusted by user pref), it'd be nice to be able to use it. Having an additional separate control seems unduly complicated to the user at first. I'd suggested it years ago (as had others) for the roadster, but it does seem unlikely in a mainstream car, and would probably catch flak in the press and with critics (debatable to what extent we should care though). On the plus side it's completely independent, so should be easier to implement and a lot less complicated than a *good* regen integrated brake pedal.
The brake pedal is obviously a candidate for the extra regen control, but if not done great, shouldn't be done at all, imo. Dangers include not only the consistent feel of the brake, but also the changing performance characteristics of the combined mechanical brake plus regen available system. Regen avail would change based on speed and battery condition. I guess in theory if braking capability (of either mechanical or regen or both) always exceeds traction then max capability wouldn't change. If it did, it'd be weird and potentially dangerous. So really just comes down to whether the control can be made to have a rock solid, completely consistent feel thought its range, even with the changing contribution of regen to the total braking force. Seems hard to get right, but sounds great if they do. I don't think it should allow smaller brakes though or it wouldn't be consistent in no regen conditions.
In addition to safety and consistent feel being "must have or don't do it" factors for me, I wonder what the practical payoff is in terms of additional efficiency possible. Obviously that'd have to be weighed against implementation cost.
On that note, most of my speed control I do with the accel, but I do often find myself wishing for a little more when slowing down coming off the freeway or other planned stops like lights and stop signs. This is both with the roadster and the loaner S's I've driven so far. I think that if I had somewhat more regen avail off the accel, then that'd almost completely eliminate the remaining habitual use of the brake pedal, and the remaining amount of "common" use is such a fleetingly small percentage that efficiency is just not a concern. Any use other than that is "oh crap" moments where efficiency is much less on my mind than worrying about my life or other property/person damage. The amount of additional regen I'd need to get to those percentages where I'd eliminate almost all the remaining non emergency braking doesn't seem like it'd impact the handling safety of sudden off pedal conditions to me, but maybe I'm wrong.
So after I've thought about all this over the years since beginning this post
(but seriously from years of roadster driving), my bottom line is that the accel pedal is perfect for routine accel/decel control, and brakes are for emergencies. If we can get somewhat more regen (maybe up to 100Kw? 120? not sure, and individual preference would vary) on the pedal that'd take care of the non-emergency brake use for me. Having any additional regen integrated on brakes is cool from an engineering standpoint, but it's not a project I'd green light if I could shove a little more in the accel pedal, given the risks of getting it non-perfect and limited actual range payoff. This does mean I'm in effect stating that the potentially large segment of the market that likes cushy coasting without keeping their foot at the correct position on the accel are basically doing it wrong :smile: and that they'll be happier once they figure out they can accomplish coasting plus better fine control if they just adjust a bit. If there's lots more regen avail but they for some reason can't put *any* more on the accel pedal, then I guess the integration with brake or a separate control becomes higher profile for me - but I can't imagine the scenario where there's more avail, but *none* of it can be at least optionally controlled with the accel pedal.
but in the time I took, the thread moved on and perhaps ironically green1 ended up saying most of the bottom line of what I was thinking, except more concisely and in a few followup posts.
…then the thread moved on again and made me feel like throwing this out there anyway :tongue:
original post:
I'd always thought Regen amount was limited by power allowed into the pack once you got past a certain speed but after talking to engineers at the D event I'm not as sure it's as limited as I thought. It sounded to me like they have increased the amount of power you can draw from the pack, at least for short bursts if not sustained. If they allow more pulled out, why not more in? Also I don't think the pack itself is the limit due to Supercharger rates, and you can see from the rates dumped to the motor on hard accel that the motor itself can use (and therefore generate?) substantially more than what we see as the current regen limit.
So, I'm more inclined to believe the current limit is based on handling effects and the desire to not surprise the crowd used to automatic transmissions in a large sedan (though would argue that the latter should be driven by user preference). Supporting the handling effects influencing current limits is that the drive train engineer spoke of more regen being available due to the two motors allowing more regen before handling was affected, and that there was a limit of how much regen could be allowed from foot off accelerator due to stability. Admittedly he did not specifically indicate that was a limit they were already hitting, but he did talk about a pet idea of his being an additional controller allowing one to manually add extra regen after foot off accelerator (like a handbrake or additional foot control). If a drivetrain engineer was mentioning this and thinking about how to do it in the context of the S rather than just an interesting idea for electric in general, it indicates to me that there may be more regen potential than what there is access to right now via the accelerator pedal. This is conjecture, but I have submitted questions to find out details. We'll see if they are answered.
Warning: wall of text thoughts to follow: tl;dr conclusion, give us as much more regen tied to accel pedal as we can safely handle as a preference setting. Assuming that's more than current, I doubt it's worth the complexity/cost/potential for failure of feel to integrate with the brake pedal.
Here's my thinking behind that though:
So if there is more regen avail, how best to access it, or should it be...
I originally thought the accel pedal was the best way to handle it, but that was when I thought there wasn't more, or at least much more, avail and that all available could be accessed without unsafe conditions being created by your foot suddenly letting off the pedal.
*If* there is more avail in excess of what could be safely put on the accel pedal (and adjusted by user pref), it'd be nice to be able to use it. Having an additional separate control seems unduly complicated to the user at first. I'd suggested it years ago (as had others) for the roadster, but it does seem unlikely in a mainstream car, and would probably catch flak in the press and with critics (debatable to what extent we should care though). On the plus side it's completely independent, so should be easier to implement and a lot less complicated than a *good* regen integrated brake pedal.
The brake pedal is obviously a candidate for the extra regen control, but if not done great, shouldn't be done at all, imo. Dangers include not only the consistent feel of the brake, but also the changing performance characteristics of the combined mechanical brake plus regen available system. Regen avail would change based on speed and battery condition. I guess in theory if braking capability (of either mechanical or regen or both) always exceeds traction then max capability wouldn't change. If it did, it'd be weird and potentially dangerous. So really just comes down to whether the control can be made to have a rock solid, completely consistent feel thought its range, even with the changing contribution of regen to the total braking force. Seems hard to get right, but sounds great if they do. I don't think it should allow smaller brakes though or it wouldn't be consistent in no regen conditions.
In addition to safety and consistent feel being "must have or don't do it" factors for me, I wonder what the practical payoff is in terms of additional efficiency possible. Obviously that'd have to be weighed against implementation cost.
On that note, most of my speed control I do with the accel, but I do often find myself wishing for a little more when slowing down coming off the freeway or other planned stops like lights and stop signs. This is both with the roadster and the loaner S's I've driven so far. I think that if I had somewhat more regen avail off the accel, then that'd almost completely eliminate the remaining habitual use of the brake pedal, and the remaining amount of "common" use is such a fleetingly small percentage that efficiency is just not a concern. Any use other than that is "oh crap" moments where efficiency is much less on my mind than worrying about my life or other property/person damage. The amount of additional regen I'd need to get to those percentages where I'd eliminate almost all the remaining non emergency braking doesn't seem like it'd impact the handling safety of sudden off pedal conditions to me, but maybe I'm wrong.
So after I've thought about all this over the years since beginning this post
(but seriously from years of roadster driving), my bottom line is that the accel pedal is perfect for routine accel/decel control, and brakes are for emergencies. If we can get somewhat more regen (maybe up to 100Kw? 120? not sure, and individual preference would vary) on the pedal that'd take care of the non-emergency brake use for me. Having any additional regen integrated on brakes is cool from an engineering standpoint, but it's not a project I'd green light if I could shove a little more in the accel pedal, given the risks of getting it non-perfect and limited actual range payoff. This does mean I'm in effect stating that the potentially large segment of the market that likes cushy coasting without keeping their foot at the correct position on the accel are basically doing it wrong :smile: and that they'll be happier once they figure out they can accomplish coasting plus better fine control if they just adjust a bit. If there's lots more regen avail but they for some reason can't put *any* more on the accel pedal, then I guess the integration with brake or a separate control becomes higher profile for me - but I can't imagine the scenario where there's more avail, but *none* of it can be at least optionally controlled with the accel pedal.
Cottonwood
Roadster#433, Model S#S37
CW,
I like that one. Consider is stolen (if you do not mind)
No theft; always happy to share observations. Please use the analogy at will!
Thank for all the work you have done to help us understand the MS!
Your premise for concluding that regen is limited to 60 kW by the battery is based on the fact that supercharger rate is limited to 120kW. This premise is inaccurate. You are ignoring the fact that regen and supercharging have totally different event time frames: seconds vs. minutes, which means that energy that battery needs to absorb during the supercharging is almost two orders of magnitude higher than energy being absorbed during the regen braking. The charging rate that battery is able to absorb over the period of time of seconds is significantly higher that the rate it can sustain over the period of time lasting minutes.
"D" variants will have total regen that is significantly higher than the regen available in the rear drive versions of the Model S.
