I get that there's a limit to regen in either scenario. My question is whether regen on the accelerator means a limit due to a person's behavior (panic lift off on the accelerator) rather than an engineering limit from the regen capabilities of the motor. In other words, if regen were applied through brake travel could the force be modulated with friction on the front brakes such that you could get safely get 90kW of regen from the rear motor. I'm just posing the question as I don't know the answer regarding why there's the 60kW limit. It could simply be driving dynamics and that's what the engineers felt was the optimum experience (rather than limits applied due to safety or electromechanical constraints).
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I get that there's a limit to regen in either scenario. My question is whether regen on the accelerator means a limit due to a person's behavior (panic lift off on the accelerator) rather than an engineering limit from the regen capabilities of the motor. In other words, if regen were applied through brake travel could the force be modulated with friction on the front brakes such that you could get safely get 90kW of regen from the rear motor. I'm just posing the question as I don't know the answer regarding why there's the 60kW limit. It could simply be driving dynamics and that's what the engineers felt was the optimum experience (rather than limits applied due to safety or electromechanical constraints).
strider
Active Member
Well we don't know and likely Tesla won't tell us. In addition to traction there are limits to how quickly the battery pack can accept charge.
But as someone who has been driving a Roadster for 4 years and a Model S for almost 2 I can tell you that based on the number of times I've had to get on the brakes hard, losing regen for that time gets lost in the noise. And I commute on US-101 in the Bay Area which has tons of traffic. Keep your eyes up and anticipate traffic. Current levels of regen work fine.
But it will be interesting if the D's have >60 regen.
I was going to say that the fact that the battery pack can handle 120 kW continuous at a Supercharger implies that the battery is not the limiting factor. But now that I think about it, the power supplied is only 120 kW when the battery is mostly discharged. Even at half charge, the power has dropped significantly - less than 100 kW I think. The limit is likely enforced for the benefit of the long-term life of the battery.
I also think that the regen limit is more than 60 kW. The biggest number on the gauge is 60, but you can get more than that. Keep in mind that the gauge is not linear. See, e.g. Tesla Model S P85 acceleration 0-215 kph on German Autobahn - YouTube
No one is saying to change the one pedal driving. It is fine to give a driver input to signal a certain amount of regen through lifting off the accel pedal.
The suggestion is to simply tap into more regen, above what is available now, and slow car harder and faster with the front wheels and the front motor. That could be built into an increased regen from lifting off the accel. But that may be too drastic of a braking effect -- especially when coming off a cruise control without depressing the accel.
So merely for acceptable driver experience the harder regen could be triggered by the brake pedal. But that is not really important. The key is to use the additional regen capability of the front wheels which is where most of the braking takes place in normal braking anyway and make electricity instead of brake dust. The front motor and use of front wheels should make that easier.
Well, certainly driving dynamics entered into it, and perhaps trumped regeneration. I've driven the regen-on-brake system for over 150,000 miles and it only took about 50 miles of driving to convince me that the regen-on-accelerator-only is far superior. I get reasonable Wh/mi numbers so I'd suspect the amount of regen lost by not having the absolute maximum regen that is technically possible is non-material (although measurable with sensitive enough instrumentation).
And one might argue it aids battery longevity not to go with "absolute max technically possible".
Has anyone argued that? That is with evidence and science? As opposed to idle speculation that seems oddly geared to simply justify and defend the status quo rather than suggest a reasonable improvement and increased efficiency?
Or one might argue that continually recharging the battery at every opportunity not only is better at giving the car a longer range which keeps the battery from discharging closer to its being empty which does effect longevity.
One might argue that we shouldn't underestimate the Tesla engineer to be bound by the limitations of past engineers in Detroit and Japan and we should encourage them to do better than their predecessors. It shouldn't be that hard to design a good feeling brake pedal that also triggers regen. The Toyota and Lexus hybrids that I have driven have had excellent braking response and it was nice to know that their brakes were mostly making electricity instead of brake dust. Most Prius' go 150k miles or more before needing any brake pads. Others have gone over 200k. Over 400K miles on original Prius Brakes? [Archive] - CleanMPG Forums
One might argue that any amount of Brake Dust = Lost opportunity to make electricity and recharge the battery.
MDK
Aussie Member
Note - I'm playing Devil's Advocate here[1] but with the new electro-mechanical brakes the "brake feel" is simulated for the friction brakes as well - "The feeling under your foot comes from the resistance of a spring and an electric motor"
That means on EM-brake equipped cars they could move some or all of the regen to the brake pedal, perhaps when the "low regen" option is selected.
- Matt
[1]I've yet to drive a Model S but regen-on-accelerator seems superior to regen-on-brakes, to me. Am looking forward to one-pedal driving.
So why not have both? some reasonable amount of braking effect comes from accel pedal lift off -- but not enough to cause the car behind you to rear end you and not enough to cause other bad driver experiences. And then have the rest of the available regen triggered by applying the brake pedal and thus getting the full regen from all four wheels driving the two motors braking to create additional regen beyond the moderate amount of regen from the accel lift off?
Only when the batteries are full, or the necessary stopping power exceeds the recharging ability of the car, would you use the old fashioned brake dust generating brakes.
same as the tesla -- from the motor being driven by the wheels. Except Toyota and Lexus design in only a little bit of regen from accel lift off driver input. The rest of the available regen (and all of it) is triggered from the driver application of the brake pedal.
This simulates the old fashioned ICE experience but it also means that the full regen can be captured up to the motor limits through even a strong application of the brake pedal rather than only up to the limits of what is an acceptable braking effect from the accel lift off.
breser
AutoPilot Nostradamus
Seems contradictory to me. If I control regen with the accelerator and with the brake then how do I know when I've gone from regen to friction brakes? Especially if Tesla works the magic to make the brake pedal have a consistent feedback?
As it is many times I find that Tesla's regen can be way too aggressive, I'm still getting used to it. So I'll realize I'm slowing down more than I want and I have to put my foot back on the accelerator. I don't really find myself going "Ohh gosh I wish I had more regen." The exception is the very tiny last bit where I'm about to stop at a stop sign or a stop light. Sure more regen would possibly bring me to a complete stop, but I doubt it's going to be that significant of regeneration since it won't last for long.
ThosEM
Space Weatherman
I'd like to support the idea of having the brake pedal do a two stage operation and propose it to Tesla:
1. First, it enhances regeneration above whatever the preset default value is.
(I'd prefer to have more than two levels of control of that as well).
2. After reaching full regen, the brake pedal begins to activate the friction brakes increasingly with increasing pressure/stroke.
(A green "Eco" light would deactivate on the dash whenever friction brakes are invoked)
I think this could be done without affecting brake pedal "feel" since the regen adjustments would be electronic rather than hydraulic. It might still be a bit tricky, but this strikes me as a much better way than doing what Cadillac did with steering wheel mounted flippers to control the regeneration strength.
Tesla have put a lot of thought into how this works, and seem to have gone for simplicity and directness. Almost all owners are very happy with the way it works; I know I am. Yes, they could do what you suggest, but I don't think you'll find much support and I don't think they'll do it.
The BMS (Battery management system) sets the charge current limit and tells the drive units what this is. This is the maximum regen. The drive units are capable of WAY more than 60kW of regen, but this is what Tesla chose to limit the off-pedal regen to probably for safety reasons. The way the drive system works, you could have just about as much regen power as you have drive power, with only the battery charge current limit being the technical limiting factor.
Tesla could very well add more regen to the brake pedal because it's a stroke simulator (on newer cars). This would require software, so it's possible we could see it someday. They do have a lot on their plate! I'd rather see lane keeping first. 60kW regen is sufficent for capture of the bulk of decel energy if you drive decently.
Tesla could very well add more regen to the brake pedal because it's a stroke simulator (on newer cars). This would require software, so it's possible we could see it someday. They do have a lot on their plate! I'd rather see lane keeping first. 60kW regen is sufficent for capture of the bulk of decel energy if you drive decently.
Between my old P85+ and my current P85D, it "feels" like the D has less regen. With the + I could use one pedal driving most of the time until 5mph, which I loved. With the D, I end up using the brakes more. It's possible with the new system that tesla has added regen to the brake pedal, so I'm actually not getting any less energy back, it's just changed the behavior and feel of the system. If there was a max setting on regen that would enable significant resistance when not on the go pedal I would use it.
caddieo
Member
I'm not an engineer or physicist and so cannot contribute to the technical minutiae that have been chewed upon in this thread. Suffice it to say that having come from ICEs where you use the brake pedal not just for abrupt/full stopping but also for gradual slowing down, it has become almost second nature to me with the S to use the brake only for rapid deceleration or full stops. At any other time, feathering the accelerator release (rather than abrupt lift-off) has been my modus operandi for handling variations in traffic flow - and I love not having to go back and forth between 2 pedals all the time. So, long question short - how would adding regen to the brake pedal affect the feel and the driving style that I have gotten used to?
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