nitramluap
Posts: 102
Joined: Thu Jul 14, 2016 12:43 am
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Re: Anybody have an brake-related accident in an i3?

Wed Sep 27, 2017 12:02 am

I33t wrote:Has BMW changed the method?

I initially accepted that the brakes were not used, but I was corrected:

http://www.mybmwi3.com/forum/viewtopic.php?t=2298

We live up on a hill. When I drive down with 100% battery, I can hear the brakes grinding, and I rarely use the brakes on the i3. Yet there is noticable wear on the front discs since 2014.

If it is not the brakes, what is making the front end noise just like brakes when I back off on the accelerator?
It's certainly doesn't seem to be the case on my 2017 vehicle. I tested this out just the other day - 100% charge and a long steady downhill (2 miles), but not so steep that the brake lights come on - the regen indicator was sitting around the A & R of 'CHARGE' on the display. My friend following confirmed that the brake lights were not on. The instrument display was showing a 'charge' during the downhill, but the battery simply sat at 100% despite having the AC on max.

I must say, I'd be really annoyed to discover that my car was riding the brakes all the way down this hill - not a smart idea! It didn't sound (or feel) like the brakes were engaged. Perhaps it's a combination of light braking and some deceleration from the motor/generator, but my brakes are still rusty at the bottom so who knows?

As far as 'protecting the battery from overcharging' from that other thread... I would have thought that this would be done at the electronics level, not simply by using brakes instead of regenerative braking because otherwise the 'power will go to the battery no matter what'. That would be a fairly clumsy & crude way of protecting the battery surely?

I33t
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Location: Australia

Re: Anybody have an brake-related accident in an i3?

Wed Sep 27, 2017 12:21 am

I'm pretty sure the brakes are applied when the battery is at 100%. There is a similar response between auto applying the brakes and the recharge, and the display shows the same when the auto brakes are applied.

My understanding is that the user has the same response from the i3 regardless, which is fair. The regen on the display probably shouldn't be showing regen when the brakes are being automatically applied.

Try using a texta on the discs and see if they are wiped off when only using the accelerator when the battery is 100%.

If the regen is created instead of brakes, there would need to be a method of dissipating the energy. Would need a heater element or something like that.
2014 BMW i3 BEV deposit placed 19th Dec 2013
Delivered in Melbourne 4/12/2014. Arrived locally 11/12/14, with 24km on the clock.

nitramluap
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Re: Anybody have an brake-related accident in an i3?

Wed Sep 27, 2017 12:52 am

I33t wrote:I'm pretty sure the brakes are applied when the battery is at 100%. There is a similar response between auto applying the brakes and the recharge, and the display shows the same when the auto brakes are applied.

My understanding is that the user has the same response from the i3 regardless, which is fair. The regen on the display probably shouldn't be showing regen when the brakes are being automatically applied.

Try using a texta on the discs and see if they are wiped off when only using the accelerator when the battery is 100%.

If the regen is created instead of brakes, there would need to be a method of dissipating the energy. Would need a heater element or something like that.
Hmm.... curious. I might try the Texta method next time I'm there. I'm not going to be happy if I discover my car has been riding its own brakes non-stop down a long hill for 2 miles! Geez...

MikeS
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Re: Anybody have an brake-related accident in an i3?

Wed Sep 27, 2017 4:50 am

My brakes are definitely applied if the car is at 100% charge when I leave me house. It is straight down hill when I leave and as I get near the bottom of the road and lift my foot off of the accelerator pedal then I can hear the brake pads on the disc.
BMW 3 Series 2005 - Aug 2014
BMW Z4 35i 2009 - Mar 2014
BMW X1 Mar 14
BMW i3 Sep 14

jadnashuanh
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Location: Nashua, NH USA

Re: Anybody have an brake-related accident in an i3?

Wed Sep 27, 2017 11:36 am

When the car is on, various things like the running lights, the HVAC, the computers, all are draining power. Regen requires there be someplace for that collected energy to go, but up to a point, it will offset the power needed to run the background stuff. Once you exceed the amount of energy available during regen, if it can't offset your load and you've released the go pedal all of the way (i.e., 100% battery, and request for max regen because your foot is off the accelerator), to maintain the same slowing rate as if it COULD put it into the battery, it begins applying the brakes instead. So, it depends on multiple things: your current load (a/c on full, fan blasting, lights on high, stereo blasting), it may never need to apply the brakes since to offset that power use, it can apply full regen...but, if lightly loaded, and max regen is requested while the battery is full, it WILL apply the brakes. IOW, it won't try to dump that power into the battery, but it will try to offset your load, but if it can't, then the brakes come on. You may not notice this until you're going down a steep hill with your foot completely off of the accelerator, but it WILL happen if the car is working right. During wet weather, it will also try to dry the rotors, but that may not be enough to actually notice and won't remove rust buildup.
Jim DeBruycker
2014 i3 BEV, 2021 X5 45e
(The i3 will be sold soon, <17K-miles, interested?)

nitramluap
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Re: Anybody have an brake-related accident in an i3?

Wed Sep 27, 2017 2:50 pm

OK. Here is what I've noticed (on my 2017 BEV anyway).

When battery is 100% the regenerative braking appears less effective, but only slightly and only at a certain point. For the most part, it feels normal. Where I do notice it is when I want the regeneration to bring me to a complete stop on a gentle slope.

For me, the hill I coast down doesn't require maximum regeneration so it's not at all noticeable to me... unless I need to slow more... but the caliper brakes definitely do not activate when I lift right off the accelerator pedal. That requires me to actually touch the brake pedal.

If I do lightly touch the brake pedal I can hear the pads engage. Mine are often a little noisy so I notice even the slightest engagement of the pads on the discs. There is also a wall on this downhill so I hear the sound reflected off this wall.

When the battery isn't fully charged, letting off the accelerator pedal seems to result in a slightly increased maximum regenerative braking effect, but because I rarely do this sort of maximum regeneration, I don't notice it.

Could it be that there is some 'space' in the battery above the reported 100% SOC which serves as a little buffer? I know that 'fully charged' isn't actually fully charged (and 0% isn't 0% either).

Maybe it's a new thing for cars with the larger (30kWh) batteries??

jadnashuanh
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Re: Anybody have an brake-related accident in an i3?

Wed Sep 27, 2017 3:41 pm

Mine's a 2014, so that could be a difference. There is a buffer at the top, and a larger battery theoretically could have enough buffer so the logic will allow some power to be put back from regen - say 200W out of 20K is one thing, but a much smaller percentage if the battery could hold 32Kw. Logically, it would be less on the smaller battery. At some point, you'd still probably have the car apply the brake, but it might take a long slope that you were coasting down before it reached that point when you started with a full battery..

About the only time I notice it is going down my driveway...there's about a 350' section that drops about 25', and not far from where I park. The brakes obviously come on every time I start with a fully charged battery. Other than that, I don't really notice that happening.

Balancing the effect of regen verses braking is tricky, and when reading reports from other cars, often not seamless. I think that BMW got it pretty well sorted. The area that does get upsetting is if you're in regen and hit a bump...the free rolling that occurs momentarily IS disconcerting, but if you're attentive, not dangerous, IMHO.
Last edited by jadnashuanh on Wed Sep 27, 2017 3:48 pm, edited 1 time in total.
Jim DeBruycker
2014 i3 BEV, 2021 X5 45e
(The i3 will be sold soon, <17K-miles, interested?)

nitramluap
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Re: Anybody have an brake-related accident in an i3?

Wed Sep 27, 2017 3:46 pm

jadnashuanh wrote:At some point, you'd still probably have the car apply the brake, but it might take a long slope that you were coasting down before it reached that point when you started with a full battery..
Yes, perhaps it would start to become apparent that the regeneration is no longer doing much if the slope was long enough and the battery was maxed out... and you'd need to use the mechanical brakes, but I'm not convinced the car *ever* applies them unless for an emergency or when using active cruise control.

I guess this regeneration behaviour with a full battery could be yet another advantage of a larger battery. All very interesting either way... and boy do I like this car!

MikeS
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Location: Brighton UK

Re: Anybody have an brake-related accident in an i3?

Thu Sep 28, 2017 8:06 am

As i said previously on my 2014 REX the brakes are definitely applied when I go down hill with 100% charge and lift the accelerator - I can hear the noise of the callipers!!
BMW 3 Series 2005 - Aug 2014
BMW Z4 35i 2009 - Mar 2014
BMW X1 Mar 14
BMW i3 Sep 14

nitramluap
Posts: 102
Joined: Thu Jul 14, 2016 12:43 am
Location: Not the USA

Re: Anybody have an brake-related accident in an i3?

Thu Sep 28, 2017 12:47 pm

MikeS wrote:As i said previously on my 2014 REX the brakes are definitely applied when I go down hill with 100% charge and lift the accelerator - I can hear the noise of the callipers!!
Well, our two 2017 BEVs never do so I guess they’ve improved it. Thank goodness too. I’m not keen on having my car ride the brakes downhill without my explicit knowledge. Brake fade anyone...?

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