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Comment by hedora | Hacker News Reader

Case in point. I thought I read bolts (volts?) sometimes put themselves into reverse and accelerate while off+charging. I wanted to paste a link, but found this article instead. It looks like this safety issue is by design. (Also, CR says the handling is “choppy” on uneven pavement, which matches my old lemon):

http://www.chevybolt.org/forum/#/topics/7778?page=1

“On this rainy morning while turning to park in a stall and so I take my food off the accelerator and expected the heavy regenerative braking. Instead it accelerated in to the stall and so I had to brake heavily and it still didn't seem to take hold. Luckily the cement parking block stopped the car albeit I still went over it.”

Response from other owner:

“Very possible for Regen to deactivate in slippery conditions. Hitting a large bump may also disengage Regen, which will feel like the car is actually speeding up (since you are expecting it to decelerate).”

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That seems crazy to disable something the use is expecting in gnarly traction situations.

In comparison I've driven our Tesla in heavy rain, snow and regenerative braking has never disabled, although traction control does take over occasionally. Tesla also gradually ramps down the braking to zero at 5mph so it doesn't suddenly disappear.

In my experiences, regen is disabled when ABS is activated

Deceleration will reduce your available traction which in most cases is better served for steering.

your case in point is that someone who wanted to park decided not to use his brakes?

is removing your foot from the accelerator instead of using the brake a standard learned behavior amongst bolt/volt owners?

I can't speak for GM cars but the Leaf regenerative braking isn't enough to stop the car in this situation, only slow it.

To me regenerative braking feels like putting the car in D3 or turning off overdrive. As soon as you stop giving enough gas to accelerate or hold speed it just drags the car down.

I would never expect it to slow the car to a stop for me.

Also in the Leaf the amount of regenerative braking applied is diminished if the car is over 90-95% charged. It has 4 dots indicating level and they have halos indicating the max possible based on conditions.

Maybe if you're used to driving manual cars and use engine braking? Sometimes I try to engine brake while the gearbox is in neutral by mistake, it's not a pleasant feeling when you don't feel yourself slow down.

If people are used to the car reacting in a certain way and it suddenly changes I'm not surprised that in can be enough to momentarily lose control. I wouldn't like that at all.

Yes, because that’s how regenerative braking works. This was discussed at length in the linked article.

That sounds dangerous. By comparison the Prius uses regenerative braking when you hit the brake, but if that isn't enough it will switch to normal (friction) braking.

Having something that switches from braking to no brake without warning seems like ... terrible design.

A Prius performs light regenerative braking whenever you're not depressing the accelerator; it primarily uses regenerative braking when using the brake pedal, but will switch to the friction brakes if you brake harder than the power train can move energy back into the battery or the battery state of charge is at the upper limit.

Uhhh, manual cars have worked like this forever. In first gear especially the braking when you let off the gas is enough to be jarring if you're not gentle

Yes, but there is no computer turning mechanical engine braking on and off based on some set of non-trivial conditions.

Ehhhh that's not quite true either.

Above a certain rpm the engine cuts fuel completely and engine braking is strong. In cars with electronic throttle control the computer might also open the throttle to maximize energy consumed compressing air.

As you pass through that cutoff range the engine starts firing again, maybe 700 rpm above idle. Engine braking stops being effective when this happens.

Also, newer cars don't do a full fuel cut when engine braking with a cold engine or if the catalyst is getting too cold to work. So sometimes engine braking isn't very strong.

Basically you can't rely on engine braking so when you're doing it your foot usually hovers on the brake pedal. This isn't any different than the hybrids

#carbureted4life

Whatever the case, I've found engine braking to be fairly consistent in manual transmission cars at a given speed/gear. But, I've never thought I could rely on it to bring me to a stop in a parking lot. It blows my mind that an EV driver would think that.

The Prius also has a one pedal B mode though which sounds similar to the L mode in this Bolt.

That's just a low-gear mode, like putting an old 3-gear automatic in 2nd gear, to engine brake downhill.

No, actually, since it's unclear how much braking regeneration will provide, when I brake I start by taking my foot off the accelerator but if I'm at all in doubt, I'll put my foot over the brake.

Also, since Tesla regenerative braking always turns off below 5 mph, I always have my foot over the brake pedal at low speeds.

Isn't engine breaking a thing that most people do or at least learn? Or can't you engine break with an automatic?

Engine breaking isn’t as effective in a torque converter automatic because the torque converter allows the engine to “free wheel” a bit. They also like to upshift pretty quickly so engine braking in a 6th gear basically does nothing. Even locking it to first or second isn’t quite the same as in a manual. Also I think some automatics will put the car in neutral sometimes when coasting. I think my Mazda 3 does this. You can definitely feel a small jolt when you are cruising down a hill on the highway and switch to “manual” mode as is it tries to engage 6th gear.

Engine breaking is common to all vehicles, especially GMs. But engine braking is almost non-existent with automatic transmissions.

Yes. Same with Tesla's default settings, and with any Toyota hybrid.

I drive a Toyota hybrid, and have never even remotely considered relying on regenerative braking to even slow my vehicle. If I want to slow down, I press the brake. If there's any slowing because of regenerative braking, I have never noticed it.

You're right now that I think a little harder about it. I used to have a 2006 Prius, and though it did charge the battery while coasting, it wasn't anything like Tesla-style one-pedal driving. I was in the habit of shifting to B while coasting down the hill where I lived, which is why I have the memory of regen braking while not pressing the brake pedal.

Pressing the brake on a Prius will use regenerative braking. It only switches to friction braking if you brake extra hard, or the battery is already charged.

So there's no need to "avoid the brake pedal to use regen" the way it sounds like these Bolt drivers are doing. Which seems really dangerous.

This makes me wonder if I actually use friction braking more than once every other month.

I've noticed this plenty:

"Hitting a large bump may also disengage Regen, which will feel like the car is actually speeding up (since you are expecting it to decelerate)."

But that's not a design fault, you're essentially using a "weaker brake" to stop, then you go over a large bump which overpowers the brake for a second. Even real brakes have that issue, but they "catch" quicker than the regen-only.

I just don't drive with L, the regen pedal allows much finer tuning.

No, the point is that the car decides on its own that the "weaker brake" will not do anything, which surprises the user.

The car doesn’t decide... physics does. The regen peddle is still engaged, it’s the jolt that overpowers the regen. It’s just physical brakes recover better from that jolt than regen.

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