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additional regen braking from the brake pedal finally?
- Thread starter bhzmark
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- Driving Dynamics Model S
I think this will prove dangerous if you are rear-ended and don't have your foot on the brake--suddenly you will find yourself out in the middle of the intersection.
I like the level of regen in the S, but worry that any extra could prove problematic on ice unless ABS throttles back regen before the rear breaks loose. Probably could safely boost to 80 or 90 with AWD.
Personally don't like having to hit the brake everytime I want more than minimal regen (eg how the Leaf works with the latest software).
The Model S does not have regen tied to the brake pedal in any way.
Source: 30,000+ miles of Model S driving between two P85s and a P85D while always paying attention to the power meter.
The power read out has *never* increased when the brake pedal was applied, even lightly.
Honestly, if Tesla shifts some % of regen to the brake pedal (pretty sure not possible with current hardware on any version) I will be pissed because that would cripple one of the best features of the car.
Source: 30,000+ miles of Model S driving between two P85s and a P85D while always paying attention to the power meter.
The power read out has *never* increased when the brake pedal was applied, even lightly.
Honestly, if Tesla shifts some % of regen to the brake pedal (pretty sure not possible with current hardware on any version) I will be pissed because that would cripple one of the best features of the car.
Once again, no one said anything about shifting moving or changing the regen on the accel.
The issue is whether to have additional regen on the brake pedal.
There is only so much regen available so if you put some on the brake pedal you'll take it off the accelerator and complicate the braking system (Have you seen Toyota's diagrams of their braking system?). Doing so would ruin the smooth braking that the Model S has. It's a bad idea.
No it wouldn't. It would be seamless. You wouldn't be able to tell the difference.
The problem is quite similar to dual motor/torque sleep: how do you get two independent systems to function seamlessly together in an instant.
There's no reason for Tesla to NOT pursue adding regen with the brake pedal, other than the fact that there may items higher up on the Pareto to which engineering resources should be directed. Presumably the ibooster can control each corner independently, so such an addition can be in rwd cars as well, not just dual motor. The algorithm just needs to ensure the proper amount/proportion of braking is applied to each wheel regardless of that braking is regen or friction.
Danal
electricmotorglider.com
I own a BEV that does exactly the thing you are saying is bad: Some regen from lifting the "go" pedal past a neutral point, some more from lifting the "go" pedal more, even more from lightly pressing the "brake" pedal, and finally full regen + whatever amount of mechanical brake by pressing the "brake" pedal harder. I, personally, don't find this 'bad'. In fact, I find it easier to use smoothly and to generate my (almost subconscious) desired behaviors in the car. Easier than the Model S that is. I find the current behavior of strong deccel from pedal lift regen, and then that deccel tapering to leaving the car rolling forward at a few miles per hour... yet on TACC it will stop... I find all that very inconsistent. In fact, I'm somewhat concerned that I'm going to tail end somebody by thinking I'm in TACC when I'm not.
Really, all of this falls into "user interface" design. Nearly everyone reading this thread trained for decades on the Idling engine and Mechanical Brake UI of the ICE, and quite a few of us on the "manual transmission" variant of that UI. What should the exact behavior of an electric be, once unconstrained by idling engine, transmission, etc. and once desirable regen is added? Opinions will vary...
Me, personally, my desired UI for all these behaviors? Auto-drive. TACC is part way there. I'm loving it.
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Only if/when regen and brakes are serialized i.e. only regen at first and then mechanical brakes later. No need to do it like that.
Break itself should behave as there is no regen whatsoever.
But if regen is set to low in settings, touching the break pedal should behave as if regen is set to normal + some additional regen power when it is safe and demanded.
Don't sell me talk how mechanical brakes always behave and feel the same. They do not.
Well, the issue with this is the the brake pedal physically controls the friction brakes. The iBooster setup doesn't magically make the pedal 100% electronic/programmable. So even if there were some way to magically find more regen (which I'm confident there is not as anyone with knowledge of how the inverter actually handles regen would also concur) then pressing the brake pedal would cause this magic/extra regen to happen along with friction braking.
It is a safety thing. The brake pedal is not drive-by-wire. The iBooster simply replaces the vacuum-assist booster with an electric-assist booster. The brakes are still hydraulic and mechanically linked to the brake pedal. The new booster still assists and has the added benefit of enabling the car to control the friction brakes as well (by actuating the brake pedal, see posts in the TACC threads). The car has no way of detaching the pedal from the brakes for any given range of motion. That would be a safety concern.
Personally, if they can find additional regen somehow (I'll state again, pretty unlikely) they should just add it to the existing regen on the lift of the accelerator.
You should be able to test this yourself by powering off the car in tow mode and keeping the fob out of and away from the car (so it doesn't turn on when the brake is pressed and activate brake assist). I bet the brakes still work when someone pushes you down a hill, albeit a bit harder to press with no assist.
It is a safety thing. The brake pedal is not drive-by-wire. The iBooster simply replaces the vacuum-assist booster with an electric-assist booster. The brakes are still hydraulic and mechanically linked to the brake pedal. The new booster still assists and has the added benefit of enabling the car to control the friction brakes as well (by actuating the brake pedal, see posts in the TACC threads). The car has no way of detaching the pedal from the brakes for any given range of motion. That would be a safety concern.
Personally, if they can find additional regen somehow (I'll state again, pretty unlikely) they should just add it to the existing regen on the lift of the accelerator.
You should be able to test this yourself by powering off the car in tow mode and keeping the fob out of and away from the car (so it doesn't turn on when the brake is pressed and activate brake assist). I bet the brakes still work when someone pushes you down a hill, albeit a bit harder to press with no assist.
Right--you'd always end up with some percentage of braking done by the friction brakes. Until the become drive by wire, anyway...
Danal
electricmotorglider.com
Nope. The first fraction of an inch of brake pedal in almost all cars causes no mechanical braking. That's the exact part of the travel, that first fraction of an inch, that causes "more" regen in my other car. It requires a firmer press to get both. And the 'transition' (which may not even be the right word) is very smooth.
Just drive a Leaf for a while to see how having some regen on the brake works in stop and go traffic. I suppose if you have restless leg syndrome it might be pleasing, but for me, I hate having to move my foot back and forth just to get the extra regen.
To add insult to injury, with the latest "upgrade" Nissan also appears to have moved considerable regen over to the brake pedal, and in addition, one now has to press the brake pedal rather firmly for a period of time to get max regen to "develop". Friction brakes are definitely absorbing a large amount of momentum which used to go back to the battery. Seems like a big waste, but I guess they did it to try to slow degradation of their thermally unregulated pack.
So, if Tesla does find a way to come up with additional regen, I vote for the one pedal application thereof. And yes, I've driven both the Leaf and the S for 3 and 2.5 years respectively, so I have some reasonable experience with both methods.
To add insult to injury, with the latest "upgrade" Nissan also appears to have moved considerable regen over to the brake pedal, and in addition, one now has to press the brake pedal rather firmly for a period of time to get max regen to "develop". Friction brakes are definitely absorbing a large amount of momentum which used to go back to the battery. Seems like a big waste, but I guess they did it to try to slow degradation of their thermally unregulated pack.
So, if Tesla does find a way to come up with additional regen, I vote for the one pedal application thereof. And yes, I've driven both the Leaf and the S for 3 and 2.5 years respectively, so I have some reasonable experience with both methods.
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Incorrect (as far as regen goes).
First, the Model S doesn't even appear to have digital knowledge of the brake pedal being depressed until it reaches the point where the mechanical brakes are to be engaged at a minimal level. This is presumably to prevent false disengaging of cruise and false brake light events during rough road drives or by lightly having your foot on the pedal in preparation for stopping. Test for yourself while using cruise control or by viewing brake lights.
On the Chevy Volt, a vehicle that uses blended regen, using DashDaq I can clearly see that regen coincides with braking completely. At no point is regen on the brake pedal independent of friction braking. The versions of the Prius I've tinkered with using the DashDaq show the same, as well as the Honda CR-Z.
There is some hybrid that supposedly did what you say at one point with a complicated drive by wire braking system, but last I recall it was no longer done because the efficiency vs cost ratio of the blended (Prius/Volt) or one pedal setup (Model S) was much more logical.
I'll just go ahead again and state that there just isn't "more regen" available to add to the brake pedal even if the hardware were there (which it isnt)
I guess the engineers on my 2000 Insight were more the "KISS" types. It gives full regen when the brake lights come on, which happens before the friction brakes engage.
I trust you on this, since you have actually studied the system and seen it. Maybe the compromise could be that, if the driver has not opted for full regen on the go pedal, it would give it with a slight pressing of the brake?
I actually was surprised this wasn't the behavior of the "Low" regen setting, honestly, in an effort to gain additional efficiency for drivers who opt for this mode. Seems simple to blend some of the available regen with braking in this case. Would change the feel of braking a little bit, but would be mostly imperceptible essentially feeling like tighter brakes.
For standard mode, however, the brakes should most certainly be brakes. An improvement I personally would like to see an option for, however, would be the reverse of this discussion. In standard regen mode, when less regen is actually available (cold, full pack, etc) have an option to automatically apply the friction brakes to compensate for the unavailable regen when lifting the accelerator. Perhaps indicated by a green power bar that fades to grey or something to show the transition. This would ensure a consistent feel to standard mode regen and seems like something that at least EV newcomers could use to adjust to the whole regen feature.
I'm not sure imperceptible is the right word here. If you have a D, changing some of the load from friction braking to regen braking means you'd be moving it from front-of-car to front-and-back; for non-D, you'd be moving the braking work from front to back.
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