Regenerative braking effect compared to traditional braking?

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HuffnPuff
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Regenerative braking effect compared to traditional braking?

Post by HuffnPuff » Fri, 16 Aug 2019, 17:35

Particularly for those who have some experience, how does the braking effect of regenerative braking compare to traditional disc/drum brakes? Especially with reference to RWD vehicles.

My understanding is that the front brakes do most of the work in an ICE vehicle and many of us have experience of yanking on the handbrake to lock the rear wheels while moving. When you have regenerative braking in a FWD vehicle one would expect that the braking force works quite well, comparable with traditional braking bias.

Hate to think what would happen after a storm when regenerative braking is not reset from max and you lift off the throttle for a quick turn.

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bladecar
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Re: Regenerative braking effect compared to traditional braking?

Post by bladecar » Fri, 16 Aug 2019, 21:03

Hi HR,
It's like you say, once you have some experience, you drive your car intelligently.
My imiev has rear wheel regen but it is not heavy regen. Still, if you regen early enough, you can slow down to say 8 kph before applying the footbrake (and confirming to whoever's behind) that you are stopping completely.
I think in your imaginary quick turn, the turn is much more violent than you would really do in that situation. If you did a really silly fast turn in anything, under any circumstances, this is what you're worried about.
Pretty sure it's the Kona which has very strong regen. The tesla has powerful regen, I believe, and will stop you.
I've seen an idiot in a ute (yute for you politicians out there) (female, just in this case :)) turn left on wet road and also do an about turn at the same time, going through 180 degrees.
I venture to say most other cars will go around that same corner mostly in an orderly fashion. It depends more on if your brain has regen or not.
I have a powerful motorcycle that has slightly hung its rear tyre out under gentle acceleration around a gentle curve. I could overcome this either by removing the engine, or understanding my machine's capabilities and staying in control.
Bung the brakes on in anything on slippery surfaces without thinking and you can attribute the outcome to drum brakes, disk brakes, regen braking, handbrakeing, or outright stupidity.

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4Springs
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Re: Regenerative braking effect compared to traditional braking?

Post by 4Springs » Sat, 17 Aug 2019, 06:12

This is interesting. I assume that regen cannot lock the wheels. This is because the retarding force is only applied when the motor is moving, and it gets less the slower the motor goes. If the wheels locked up then the motor would be stationary, and the regen wouldn't work. A sort of natural ABS.
In practice a very aggressive regen on a very slippery surface should result in the wheels slowing down but not stopping. They might still slip though? I'm not sure if it would be possible.

My experience is with a Mitsubishi Outlander. The regen on this vehicle is 'reasonable' - it is a heavy vehicle with a small battery. It provides more than the engine braking you get from a manual ICE vehicle, but not as hard as heavy braking. The effect decreases markedly as you slow down, getting gentler the slower you go. In the Outlander you get a certain amount of regen when you lift your foot off the accelerator, but to get the maximum you have to put your foot on the brake pedal. I'm not sure if the regen comes from the front wheels, rear wheels or both. But after only a few minutes driving you get used to how it feels, so I can't imagine that you'd 'forget' about the regen, any more than you forget about the retarding force of your ICE engine braking. In your scenario of lifting your foot of the accelerator for a quick turn, the effect is the same as when you lifted your foot off the accelerator 30 seconds ago for the last turn.

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bladecar
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Re: Regenerative braking effect compared to traditional braking?

Post by bladecar » Sat, 17 Aug 2019, 07:46

Just to try a slightly more useful reply, you may be talking about the level of regen you will programme the vehicle to have.
When I was buying the Blade car, I was initially told I could have any regen amount I wanted, which simply meant that it was adjustable.
I was immediately told after that there was a general limit that they would set it to for usability purposes (my words).
I always liked the idea of massive regen (without regard to technicalities) to be able to scream to a halt and get all that energy back :)
So I'd imagine you would set regen to slightly more (for the above reasons) but only use that as a starting point and run you car around a sand covered concrete curve with plenty of runoff on private property etc etc, taking great care, and vary it, if this is where you are coming from.
Acquired thoughts on regen are. Yes, you're getting energy back into your system (much more useful on long trips where you may be relying on it to maximise range) but you don't get a huge amount back (I know every little bit helps, and I know you're not using mechanical items that need maintenance, like brakes).
If you have rear wheel drive, then the rear tyres take the brunt of acceleration as well as braking via regen, and have accelerated wear.
If you have front wheel drive, then the front tyres face acceleration, regen and turning wear.

I'm starting to see regen as great for reducing the need for mechanical brake maintenance, more than anything else.

I drive the ev mostly gently. I try to use no more than half power gauge reading except when I get annoyed with something and 'flatten' it to move to a better location on the road (around town). Towards the lights, I regen-brake quite early if there are no vehicles behind me, and fairly early otherwise. I take my foot off the throtle to the extent that regen is building and only that far (you ev people know that feeling that regen builds as you let the foot off the throttle but at some point it doesn't build any more). In the other lane, I see the idiots doing what I do in an ice car, accelerate at the normal rate of the particular car, hurtle towards the already going to red lights and then stop the car within its usual ability. In good words, all over the top.
They're destroying their tyres and their brakes, and chewing fuel. It's all good, just all too much. Also nothing worse than the dills who drive like it sounds like I do, slowly move away, get to 10k's under the speed limit, stay at that speed no matter what, and give the impression they aren't quite sure what they're going to do next. But I don't do that, I just do everything more gradually, not more slowly, because I stay aware of my surroundings (bike rider, see) and behave the same as everyone else if I happen to be stuck in that traffic location.

Maybe this has been more useful (spelt 'tedious' :))

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Re: Regenerative braking effect compared to traditional braking?

Post by mikedufty » Sat, 17 Aug 2019, 13:49

Regen is not on or off, it's proportional to the accellerator position, so the same as regular brakes, will only cause a problem if you use too much at the wrong time and place. The i-miev regen is no stronger than manual engine braking. I think other cars have more, but I don't know if any have enough to make locking the wheels an issue (assuming not on ice or mud).
I have skidded the rear wheel with (ICE) engine braking on motorcycles a few times, but needs a lot of rev's and for the rear to be unweighted by the front brakes as well. Not really a problem. Interesting though as like regen, it can't actually make the wheel lock (stop rotating) but as long as it is rotating slower than the vehicle is moving, it still skids.

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jeffthewalker
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Re: Regenerative braking effect compared to traditional braking?

Post by jeffthewalker » Sat, 17 Aug 2019, 15:12

When the wheels are barely or not moving you can electronically apply forward or reverse power to brake or hold on an up/down slope without using mechanical brakes.
It is hard to make predictions, especially about the future. Yogi Berra

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bladecar
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Re: Regenerative braking effect compared to traditional braking?

Post by bladecar » Sun, 18 Aug 2019, 11:02

I have skidded the rear wheel with (ICE) engine braking on motorcycles a few times, but needs a lot of rev's and for the rear to be unweighted by the front brakes as well. Not really a problem. Interesting though as like regen, it can't actually make the wheel lock (stop rotating) but as long as it is rotating slower than the vehicle is moving, it still skids.
[/quote]

Yes, I wasn't clear with the motorcycle reference. I was saying that any behaviour by a vehicle is learnt by a persistent driver in different circumstances and they must use that experience to drive sensibly for those circumstances. I was talking about acceleration for the motorcycle and needing only one experience to learn from it. Later I realised that HuffPuff may have been really focused on what level of regen to set for a rear/wheel drive vehicle.

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