Regen braking to stop? (similar to BMW i3)

[Uncle Paul]

Really splitting hairs here. Both systems work pretty well to those used to them. Tiny gains either way...mostly emotional

 

[Jeff N]

The i3 "regen to a stop" design sounds very similar to what GM is doing in the Bolt EV if you drive in 'D' and use the steering wheel regen paddle or shift into 'L' and lift off of the accelerator.

 

[jerry33]

I would love a regen-to-stop capability. Make it an option in the settings at least.

This is one of those "be careful what you wish for" items.

 

[timf]

I thought the brake lights stay on. You confirmed they don't? I seem to recall checking they did, but that was early on, it's possible that was changed with a later software update. Still, that doesn't seem like a valid reason from a design standpoint--the computer should be able to smooth all of that out and it be invisible to the user.
...
I had the Model X overnight, and I noticed at least once that when I took my foot off the brake it started rolling back slightly. Maybe because it's so heavy?

My reference is looking at the reflection in cars behind me at night. It appears that the brake lights only stay on when you are actively regenerating, and as soon as the car comes to a stop the brake lights go off unless you are holding them.

This video demonstrates it well:

Look at 1:41 for confirmation of my concern.

In certain circumstances the Model X may not go into Hold mode, but it's clearly indicated on the dashboard when you are by a ((H)) icon. It should never roll backwards when in Hold mode, but I haven't tested it on any significant slopes.

 

[jerry33]

My reference is looking at the reflection in cars behind me at night. It appears that the brake lights only stay on when you are actively regenerating, and as soon as the car comes to a stop the brake lights go off unless you are holding them.

The brake lights on regen braking are triggered by deceleration. If they weren't they would flash all the time. As it is, it works just about perfect. If you are braking hard with regen the lights come on, which is what you want to alert the other drivers. In 70+K miles I've had zero issues with cars behind me not understanding what I did.

This is truly a non-issue.

 

[ThosEM]

Wouldn't total non-use of the braking system cause (over time) issues with the hardware? I'm thinking of rusted disks, sticky calipers, etc.

Yes, I've read some complaints here in the forums ("Ouch! First huge repair bill") about brakes getting stuck (frozen actuator cylinders) owing to disuse and corrosion. The fix can be very expensive. So it's definitely a good idea to routinely use the brakes for holding and faster deceleration than possible with regen.

 

[eye.surgeon]

You can see when you r rear brakes are on by looking at the car image on the instrument display. They stay on when the car is stopped with "hold" activated. but that's not my issue, I want regen to persist until the car stops.

 

[jerry33]

You can see when you r rear brakes are on by looking at the car image on the instrument display. They stay on when the car is stopped with "hold" activated. but that's not my issue, I want regen to persist until the car stops.

Any particular reason? Under about 10 km/h there is almost no kinetic energy to capture (given that regen doesn't capture it all). So the way to do it would be to simulate regen by using power from the battery to slow down the motor. Sounds inefficient to me.

 

[gfb107]

I think the idea is to have the software engage the brakes so the car will come to a complete stop without having to step on the brakes.

 

[Fresh Start Detail]

Interesting discussion. I've driven both Teslas and i3's but only for very short distances; I was a bit "clumsy" when coming to a full stop the first few times I drove both cars. Now after reading this I want to get back in an i3 to really compare.

 

[eye.surgeon]

Any particular reason? Under about 10 km/h there is almost no kinetic energy to capture (given that regen doesn't capture it all). So the way to do it would be to simulate regen by using power from the battery to slow down the motor. Sounds inefficient to me.

I would disagree that a 5,000 lb car slowing from 10 km/hr to zero has no kinetic energy to continue to recharge the battery. Try stopping your car with your bare hands at 10 km/hr and see how much kinetic energy it dissipates into you.

 

[jerry33]

I would disagree that a 5,000 lb car slowing from 10 km/hr to zero has no kinetic energy to continue to recharge the battery. Try stopping your car with your bare hands at 10 km/hr and see how much kinetic energy it dissipates into you.

You have to consider the losses, what's left is very little, so the rate of stopping will need additional power input to keep the same deceleration.

 

[tonyx]

How many stops does one come to EVERY trip? I would prefer a gentle stop without having to depress the brake pedal, even if it takes a small amount of energy, as it very much simplifies the driving experience.

On the shifter design, I would argue that while Tesla's shifter is a bit old school, the i3 shifter looks like a tumor growing out of the steering column, and would not want that thing in my Tesla...

 

[jbcarioca]

This thread is fun! I have driven an i3 quite a bit, although I have not bought one because they sell only the REX in my market and I do not want the ICE maintenance headache. Between them I do see apples and oranges in some respects, primarily because the BMW seems to be a BMW-style technology tester (I have had one, the X1) with some features that are not really mature, and a bit of a rebellious approach.

The Tesla tries to be more conventional in feel, it seems to me, and mostly succeeds in making it quite MB-like in controls (apart from the giant screen, of course).

I think these two are so different that they really do not compare, other than in source of motive force. Therefore i will only say I personally quite like them both.

 

[David99]

It's not about energy at all. There is very very little energy below 5 mph. So regen can't capture it and programming the motor/inverter to come to a complete stop would use very very little energy. It has also nothing to do with making sure the brakes are used. Tesla already uses the brakes to come to a stop when TACC is active.

It's a choice by Tesla to fade out regen and force people to switch to the brake pedal. There is no technical reason, or energy concern one way or another. The Model S (and X) is perfectly capable of coming to a stop smoothly using both regen and brakes. Using TACC shows that. Tesla just doesn't want to do it. BMW thinks its a great option and people seem to love the way it behaves. It makes perfect sense to have the car come to a stop in a sense of true one pedal driving and having to switch to the brake pedal is inconsistent with that.

Another thing that BMW got right is using the brakes to keep regen consistent at 100% charge. Tesla's regen fades and gives the driver often an unexpected inconsistent feeling. Since Tesla is perfectly capable of having regen and brakes work together in harmony (TACC and AP) they just forgot about regen when the battery is near full.

Having acceleration and coming to a stop on one pedal would also make going in and out of parking spots easier. Currently you have to use both pedals or you use creep mode and modulate using the brake pedal. How stupid that when going to very slow speeds you drive the car with the brake pedal!

So in every aspect it makes a lot of sense to have the car come to a stop using one pedal and be consistent in all situations.

 

[jbcarioca]

I...

So in every aspect it makes a lot of sense to have the car come to a stop using one pedal and be consistent in all situations.

I agree with you except for your last sentence. In one sense, an important one, a single pedal normal operation is problematical. That is that no other motor vehicles normally operate in a single pedal fashion, and the braking function needs to be an instantaneous nearly reflex action by drivers to cope with emergency situations. Until there is level 4 autonomous driving the recourse to the driver must be absolute.

Such an approach is slightly less convenient than a single pedal, no argument. I personally would like it better.

But, until such a time as Level 4 arrives think the Tesla approach is the safer one, thus the proper one.

 

[bxr140]

In one sense, an important one, a single pedal normal operation is problematical. That is that no other motor vehicles normally operate in a single pedal fashion, and the braking function needs to be an instantaneous nearly reflex action by drivers to cope with emergency situations.

I think there's some confusion. You identify two different driving conditions above: Normal vs emergency. D99 is referring to the former where, from a safety perspective anyway, having consistent off throttle decel is certainly better. There are plenty of non-emergency situations where pucker factor gets elevated a step or three when off throttle decel doesn't respond as expected.

I don't think there's any debate that the later requires the brake pedal.

 

[jerry33]

I think there's some confusion. You identify two different driving conditions above: Normal vs emergency. D99 is referring to the former where, from a safety perspective anyway, having consistent off throttle decel is certainly better. There are plenty of non-emergency situations where pucker factor gets elevated a step or three when off throttle decel doesn't respond as expected.

I don't think there's any debate that the later requires the brake pedal.

Even the first one might require a brake pedal in some cases. I suspect it's better to to know that you will have to press the brake pedal to come to a complete stop. That way you'll be thinking about it (even if only subconsciously) and it becomes a habit.

 

[bxr140]

Even the first one might require a brake pedal in some cases.

For sure, and consistent off throttle decel allows us to better anticipate when we need to use the brake pedal.

I suspect it's better to to know that you will have to press the brake pedal to come to a complete stop.

Probably true, at least in the present day.

As autonomy matures and becomes more consistent, more vehicles will be able to stop themselves smoothly and safely. I've only had an autopilot loaner so I can't comment on how effective today's Tesla is at this. I'm certain tomorrow's Tesla will do it flawlessly.

 

[Curbine]

I agree with you except for your last sentence. In one sense, an important one, a single pedal normal operation is problematical. That is that no other motor vehicles normally operate in a single pedal fashion, and the braking function needs to be an instantaneous nearly reflex action by drivers to cope with emergency situations.

Absolutely. I think the fact that BMW made a car with only an accellerator and no brake pedal is a major safety hazard. I simply cannot believe they got approvals from the government to release such a dangerous vehicle!

On a serious note, the reason that Teslas use the brake pedal like an ICE vehicle is because people are used to it. BMW's system is absolutely superior from a user experience and safety issue (debate energy savings or whatever as much as you like) and their decision to implement one-pedal driving has hurt them. Yes, hurt them--because it takes a few days to completely wire your brain to understand how it works and be able to drive and stop smoothly. On a test drive, there's so much that's not normal about the i3 that for many people it is a turnoff.

The i3 looks like a compact econo-mutant car. But it's rear wheel drive. It's light as a feather, and therefore crazy fast. (the non-REX feels best) The steering is tight, but you might call it twitchy if you're used to normal cars. The one pedal driving feels strange. The regenerative braking is super aggressive. The doors are strange. The look is strange. It's too much all at once--I'm sure that hurt them in sales because it's hard to get the average person to try it out and fall in love it with. That takes a few days.

The statement that it's dangerous is just so crazy sounding--what is the context? "Learning" to drive an i3 is easy and safe, as taking your foot off the accelerator to hit the brakes starts slowing down dramatically even before that 0.5 seconds you get over to the brake pedal. I would suggest that it's way more dangerous to drive a manual transmission car than an i3--would you agree?

I think the i3 is an amazing car, wonderful achievement. I would have told BMW to not do so much at once to have better marketing success (why not just make an electric x3?), but I'm glad they made it so I can have one. I also love my manual transmission sports car at the opposite end of the spectrum. And I am looking forward to getting a Model X--even if they don't adopt one pedal driving. (though I really wish they would, it's so nice for low speed driving like parking lots)