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2010 2011 BMW 5 Series Forum F10 BMW 5-Series (F10) Forums General 5-Series Sedan and Wagon (F10 / F11) Forum Brake Energy Regeneration?
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      09-14-2013, 11:15 AM   #1
FnoFFen
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Brake Energy Regeneration?

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My car has this, but I don't really know what this is.

I suppose it charges the battery when I am applying the brakes? However, at low speeds I feel the car brakes slightly when I am letting go of the accelerator (I don't use the auto-hold). Is that part of this system? It is quite annoying and I would like to turn this function off if possible.

Last edited by FnoFFen; 09-14-2013 at 11:16 AM.. Reason: Forgot some information
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      09-14-2013, 12:22 PM   #2
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I'd call it more an intelligent alternator. I think the way it works is by using braking effort (or non power) it can avoid the drain on the engine at other times to give you the power or economy.
I know what you mean about the slowing down though. Foot off the gas and it changes down the gears which is not that smooth.
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      09-14-2013, 03:38 PM   #3
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Quote:
Originally Posted by FnoFFen View Post
My car has this, but I don't really know what this is.

I suppose it charges the battery when I am applying the brakes? However, at low speeds I feel the car brakes slightly when I am letting go of the accelerator (I don't use the auto-hold). Is that part of this system? It is quite annoying and I would like to turn this function off if possible.
The 'regeneration' is not connected to the brakes, it is as said, an intelligent alternator.

I can't understand how you feel it, as in my 535i (when showing as charging on the display, on the overrun when it kicks in) there is no sensation back through the drivetrain at all. All silky smooth, as is the down changing of the gearbox.

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      09-14-2013, 07:13 PM   #4
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Quote:
Originally Posted by HighlandPete
Quote:
Originally Posted by FnoFFen View Post
My car has this, but I don't really know what this is.

I suppose it charges the battery when I am applying the brakes? However, at low speeds I feel the car brakes slightly when I am letting go of the accelerator (I don't use the auto-hold). Is that part of this system? It is quite annoying and I would like to turn this function off if possible.
The 'regeneration' is not connected to the brakes, it is as said, an intelligent alternator.

I can't understand how you feel it, as in my 535i (when showing as charging on the display, on the overrun when it kicks in) there is no sensation back through the drivetrain at all. All silky smooth, as is the down changing of the gearbox.

HighlandPete
Highland, I agree with you. I think what throws people for a loop is precisely that "silky smoothness."

In most non-BMWs, releasing the accelerator will pretty much leave you at speed for a few monents---depending on gradient, etc.

But, releasing the accelerator on a BMW, at speed, noticeably slows you down. You almost feel a pull in the opposite direction.

This does not occur if you have the new system that throws you into neutral whilst in Eco Pro under specific conditions.
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      09-15-2013, 01:02 AM   #5
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I've noticed this, if you take your foot off the gas to coast to a stop for say traffic lights, the gearbox changes down the gears and you get engine braking which is not that smooth. Compared to my previous e39 , its not as smooth although i think that car would stay in 2nd gear rather than go onto 1st ( unless in d/s mode)
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      09-15-2013, 02:57 AM   #6
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The new LCI has a sailing mode when in ECO PRO mode. This makes the gearbox go "free wheeling" when the accelerator is released.
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      09-15-2013, 03:00 AM   #7
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Quote:
Originally Posted by AP View Post
I've noticed this, if you take your foot off the gas to coast to a stop for say traffic lights, the gearbox changes down the gears and you get engine braking which is not that smooth. Compared to my previous e39 , its not as smooth although i think that car would stay in 2nd gear rather than go onto 1st ( unless in d/s mode)
It is virtually the opposite in my 535i, the engine drops back to around 1,000rpm before it down changes (then only increases by about 200rpm or so) when slowing to a junction. Say I'm coasting down from 60mph to a restricted zone, typically I have to touch my brakes if following others doing the same, as the car runs so freely (compared to other cars) on the overrun.

I do believe some of the differences we find are in the use of the throttle pedal. Speed of pedal movement, (same for the brake pedal) does change the gearbox characteristics. But with a slow lift off of the pedal there is no forced down changing in my car. Clearly observe the regeneration feature being displayed, again without any feel to it.

Drive harder and the gearbox wakes up, as I'd expect it to, but still exceptionally smooth.

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      09-15-2013, 12:19 PM   #8
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Mines like Petes, it doesn't seem to slow at all when lifting off the accelerator and coasting and Ive never even noticed the down changes they are that smooth.
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      09-15-2013, 04:11 PM   #9
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Quote:
Originally Posted by FnoFFen View Post
My car has this, but I don't really know what this is.

I suppose it charges the battery when I am applying the brakes? However, at low speeds I feel the car brakes slightly when I am letting go of the accelerator (I don't use the auto-hold). Is that part of this system? It is quite annoying and I would like to turn this function off if possible.
My LCI 528 does exactly the same thing. At highway speeds, the car feels like it's "sailing" when you take your foot off the accelerator, but at low speeds, like driving through a parking lot, there is an immediate and not so subtle deceleration when you take your foot off of the accelerator. I really dislike the feeling. It's almost feels like the emergency brake is slightly on. I let a friend drive my car and she immediately complained about the feeling. I wish whatever is causing it could be disabled.
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      09-15-2013, 04:43 PM   #10
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Its not the regenerative braking, its the transmission downshifting. Its trying to slow down the car with engine braking, a lot of performance cars are program like this, you just have to get use to it.
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      09-15-2013, 10:22 PM   #11
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First post .. finally

In my vehicle '12 528xi and also being my first BMW and car with regenerative breaking, I dont mind the behavior at higher or even mid speeds. Where I do mind it is when I drive down the first part of my driveway, which has like a 15 degree pitch I tend to just lift my foot off the gas.

At first I coast, but then almost lunge as the regeneration light kicks in. I havent paid attention yet whether it shifted gears. I just wish the lunge wasnt there. This never happens in higher gears or speeds.
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      09-16-2013, 02:11 AM   #12
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I suppose that what you are describing is engine braking during coasting. If you come from a manual trans car you would be familiar with it. The BMW ZF 8-speed is cleverly programmed and uses engine braking more so than a traditional slush box. Engine braking is a good way of decreasing brake wear. What BMW also does is to clutch the alternator so that it mostly is driven only during engine braking. That way, no fuel is used to charge the battery.

To create a smooth transition between downshifts and engine braking, the software lets the engine run between shifts and then after a second or so you can feel the engine braking effect (and also see the regen bar light up). If it went straight to engine braking and downshift at the same time, you would feel a jerk as the lower gear engaged. That's due to a much "tighter" torque converter that doesn't allow as much slip as old school converters.

It's kinda like being smooth with the clutch pedal on a manual trans as opposed to just taking your foot straight off the pedal during a downshift.

The same effect is also present during coasting when you stay in the same gear. It tries to create a smooth transition and not go straight to engine braking.

The 8-speed auto feels much more like a manual trans since the torque converter is much more direct than old slushbox autos.

I actually like how direct and responsive the transmission feels compared to many other autos. In Sport mode that effect is even more pronounced and my car almost feels "jittery" to throttle pedal input at certain speeds. In the M5/M6 in "M-mode" this effect is so pronounced that it's almost hard to drive at a steady speed in low speed twisty road conditions. IMHO, it makes the car feel alert and ready
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      09-16-2013, 03:35 AM   #13
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Interesting comments and some opposing experiences.

I wonder if some of the differences are the gearbox mode we are using?

I'm referring to being in 'D' normal/comfort mode. Where there is no down changing for any engine braking at lower speeds, rolling down to a junction. As previously stated the engine drops to around 1,000rpm and then smoothly down changes without any lurch, jerkiness or lunging, nothing like that at all.

Sport mode is a different animal, as we would all expect, as it must down change to keep up some revs. Therefore can lose some of the silky smoothness.

I've driven a good few examples of 5, 6, and 8-speed boxes and never had one gearbox that behaves any different coasting down to a junction in 'D'. I know other drivers have had the jerkiness and even the 'slam' issue in 'D', (particularly the 6-speed autobox), but that was/is a problem not the norm.

Descending slopes/hills and lifting off the gas will instigate a down change (or two), again that is normal. But is typically dependant on speed of pedal lift off. Same as a quick jab on the brakes will instigate down changes on a slope.

Interested to see if all the experiences are when using 'D' the normal/comfort modes.

HighlandPete
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      09-16-2013, 07:41 AM   #14
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Quote:
Originally Posted by HighlandPete View Post
Interesting comments and some opposing experiences.

I wonder if some of the differences are the gearbox mode we are using?

I'm referring to being in 'D' normal/comfort mode. Where there is no down changing for any engine braking at lower speeds, rolling down to a junction. As previously stated the engine drops to around 1,000rpm and then smoothly down changes without any lurch, jerkiness or lunging, nothing like that at all.

Sport mode is a different animal, as we would all expect, as it must down change to keep up some revs. Therefore can lose some of the silky smoothness.

I've driven a good few examples of 5, 6, and 8-speed boxes and never had one gearbox that behaves any different coasting down to a junction in 'D'. I know other drivers have had the jerkiness and even the 'slam' issue in 'D', (particularly the 6-speed autobox), but that was/is a problem not the norm.

Descending slopes/hills and lifting off the gas will instigate a down change (or two), again that is normal. But is typically dependant on speed of pedal lift off. Same as a quick jab on the brakes will instigate down changes on a slope.

Interested to see if all the experiences are when using 'D' the normal/comfort modes.

HighlandPete
My experiences in "D" are exactly the same as yours. Agree with everything you wrote.
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      09-16-2013, 08:17 AM   #15
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It really depends on what the driver is use to driving or what their previous cars are. If one come from an non-performance car or even a Mercedes, the down shift will take a while to get use to. If your last few cars were performance sedan or stick shifts, it is almost a natural transition. All of my BMW and Audi did this, downshifing when coasting and my last BMW and Audi did not have regenerative braking. I suppose how agressive a tranny downshift depends on one's driving style just like how the tranny up shifts. The adpative transmission will learn and up/down shift accordingly. A couple of things to try here is one might want to shift the transmission to neutral when braking to confrim that its the tranny that is slowing down the car and you can also try reseting the transmission and see if the downshifting improves.

For those of you with new cars, it will take a while for the drivetrain to lossen up. Thats decelaration when you let go of the gas is probably the drag from the new powertrain.

Last edited by The X Men; 09-16-2013 at 03:07 PM..
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