Will regenerative braking cause accidents?

[Paul-a594r]

Evening

Had a thought tonight whilst driving my Mrs E Golf. Will regenerative braking cause accidents? The E Golf has decent regenerative powers, that slow's the car down fairly quickly, BUT, I'm guessing the brake lights don't show? If someone is up your arse and you don't realise, surely there's a possibility of being rear-ended?

Has this happened to anyone yet?

[MitchT]

As I understand it regenerative braking happens when you press the brake pedal, so the brake lights will illuminate. The car works out how much traditional braking is required in addition to the regenerative braking to provide adequate retardation. I can't imagine the car will activate regenerative braking when you've lifted off to coast as you're not specifically commanding the car to slow down.

[md_ph]

Paul-a594r said:

Evening

Had a thought tonight whilst driving my Mrs E Golf. Will regenerative braking cause accidents? The E Golf has decent regenerative powers, that slow's the car down fairly quickly, BUT, I'm guessing the brake lights don't show? If someone is up your arse and you don't realise, surely there's a possibility of being rear-ended?

Has this happened to anyone yet?

If your in B mode then it lights up the brakes when it’s slowing the car down.

I wondered this also and got my wife to follow me and whilst talking on the phone she was able to confirm they lit up.

[md_ph]

MitchT said:

As I understand it regenerative braking happens when you press the brake pedal, so the brake lights will illuminate. The car works out how much traditional braking is required in addition to the regenerative braking to provide adequate retardation. I can't imagine the car will activate regenerative braking when you've lifted off to coast as you're not specifically commanding the car to slow down.

Not if you have the gear selector in B mode, through the city centre you can nearly drive with 1 pedal, when you let off the throttle it actively brakes for you using the motor/s to slow you down.

[MitchT]

Interesting. Reminds me of one of those kiddy bikes that doesn't coast when you stop pedaling!

[ZesPak]

MitchT said:

Interesting. Reminds me of one of those kiddy bikes that doesn't coast when you stop pedaling!

Look up "one pedal driving".

Basically lifting the throttle slows down the car faster than it would normally do. It takes a bit of getting used to but after a first drive it feels completely natural. In fact, coasting feels "off" now if I drive the QV!

As for the OP's question: I know most -if not all- ev's will light up the brake lights at certain deceleration. So in essence it'll be safer than a manual car, which you can engine brake without lighting up the brake lights.

I'm sure there:

1. are ev's that don't do this
2. will be legislation to make it mandatory

[xx99xx]

Here you go:

https://www.unece.org/fileadmin/DAM/trans/main/wp2...

If you don't fancy reading all 96 pages, refer to UNECE 13H.

To summarise:

5.2.22.4. Electric regenerative braking systems as defined in paragraph 2.17., which produce a retarding force upon release of the accelerator control, shall generate the signal mentioned above according to the following provisions:

Vehicle decelerations

Signal generation
≤ 0.7 m/s² The signal shall not be generated
> 0.7 m/s² and ≤ 1.3 m/s² The signal may be generated
> 1.3 m/s² The signal shall be generated

In all cases the signal shall be de-activated at the latest when the deceleration has fallen below 0.7 m/s².

[chrispmartha]

MitchT said:

As I understand it regenerative braking happens when you press the brake pedal, so the brake lights will illuminate. The car works out how much traditional braking is required in addition to the regenerative braking to provide adequate retardation. I can't imagine the car will activate regenerative braking when you've lifted off to coast as you're not specifically commanding the car to slow down.

That’s not how it works in some EVs, the polestar brakes when you lift off the accelerator. I have touched the brake only once or twice since getting it, its that effective and actually becomes really natural after no time at all.

Im not sure if it activates the brake lights though. I would imagine it does.

Edited by chrispmartha on Thursday 25th March 07:44

[Heres Johnny]

As touched upon there are two basic approaches

Lift off regen which at its best is one foot driving. Some like it for its simplicity although its not so good for good car control or spirited but still defensive driving where you might want to say cover the brake when you approach a junction as lifting off slows you down. Its also harder to find a neutral power position as it effectively requires some throttle to do so. But its great the way most people drive around town. Can also be inconsistent depending on temperature of the battery and the amount of available regen - so sometimes you lift off and no stopping occurs at all.

Regen on brake. Harder to implement as the transition from just regen braking to the addition of mechanical braking is not always progressive, but drives more like a traditional car and pedals do what they have always done. Tends to be more on the more performance orientated cars like the taycan and the bmw i8 from my experience.

Whichever way it does it though, brake lights come on if the car is slowing beyond a given threshold. What I found, and it takes some time is to get used to with one foot driving cars, is finding the "easing off" the gas position without putting the brake lights on, it can happen after an overtake, on motorways where if you're gaining on traffic you might back off to lose speed etc, but do it too much and you end up accidently flashing your brakes at the car you've just overtaken.. not cool.

[ZesPak]

[Mr E]

ZesPak said:

As for the OP's question: I know most -if not all- ev's will light up the brake lights at certain deceleration. So in essence it'll be safer than a manual car, which you can engine brake without lighting up the brake lights.

I'm sure there:

1. are ev's that don't do this
2. will be legislation to make it mandatory

My gen1 lead does not illuminate the brake lights when I lift, and in ‘B’ mode the retardation is significant.
I am aware of it, and usually watch the rear view in case the car behind starts getting big

[kambites]

Mr E said:

My gen1 lead does not illuminate the brake lights when I lift, and in ‘B’ mode the retardation is significant.
I am aware of it, and usually watch the rear view in case the car behind starts getting big

So how does that get around UNECE 13H quoted above? It should have failed EU type approval. Or can it not exceed 1.3m/s/s under regenerative braking?

Edited by kambites on Thursday 25th March 09:32

[Mr E]

kambites said:

So how does that get around UNECE 13H quoted above? It should have failed EU type approval. Or can it not exceed 1.3m/s/s under regenerative braking?

Edited by kambites on Thursday 25th March 09:32

Unknown chief. Presuming those regs are mandatory (or are reflected in legislation that is), either the car doesn’t breach 1.3ms^-2 or it’s broken.

[kambites]

Mr E said:

Unknown chief. Presuming those regs are mandatory (or are reflected in legislation that is), either the car doesn’t breach 1.3ms^-2 or it’s broken.

Yeah the regs appear, as far as I can tell, to be part of the type approval process. I suspect early Leafs sneak in under the 1.3m/s/s figure. I don't remember they having particularly strong regen?

[Mr E]

kambites said:

Yeah the regs appear, as far as I can tell, to be part of the type approval process. I suspect early Leafs sneak in under the 1.3m/s/s figure. I don't remember they having particularly strong regen?

Regen is sufficient that I changed the front discs and pads at 40k because they were badly corroded. I barely use the brakes most of the time.

We’re talking ~0.13g here, so not huge amounts but sufficient that a lift at 80mph will drop the car to 50 quickly enough that I worry about the guy behind.

I wonder what a fully closed throttle at 5k rpm in 3rd gear would generate in a modern turbo diesel.

[ZesPak]

kambites said:

So how does that get around UNECE 13H quoted above? It should have failed EU type approval. Or can it not exceed 1.3m/s/s under regenerative braking?

Quite possibly the Leaf, which was a very early EV, predates that line in the type approval.
Just like you now have type approval for the sub 30km/h sounds in EV's, everything pre mid-2019 doesn't have them or need them.

[kambites]

ZesPak said:

Quite possibly the Leaf, which was a very early EV, predates that line in the type approval.
Just like you now have type approval for the sub 30km/h sounds in EV's, everything pre mid-2019 doesn't have them or need them.

The rule appears to date from 1995. The Leaf isn't quite THAT old!

[Mr E]

kambites said:

The rule appears to date from 1995. The Leaf isn't quite THAT old!

I’d believe it from some of the interior plastics.

[kambites]

Mr E said:

I wonder what a fully closed throttle at 5k rpm in 3rd gear would generate in a modern turbo diesel.

More than that, I think, but it'd be a moot point because in that case the following driver wouldn't be able to see the brake lights through the clouds of smoke anyway.

[dapprman]

I think there's a far higher chance of someone used to regen braking having an accident the next time they jump in to a car with far lighter levels of it. I know I almost got caught out - been driving my Zoe50 in B mode when I jumped in to my Lexus, which I drive in Eco mode - you notice it reclaims energy when you take your foot off the accelerator, more so than in normal/sport mode, but it's minor compared to the Zoe - I neded up approaching a junction a little quicker than i expected (though with enough time to act). It's the fact I knew there was regen braking, just expected a lot more that almost caught me out.