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      07-02-2014, 11:40 AM   #1
zeevette
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Brake assist disable

I really am starting to hate what the salesman told me was "brake assist". As I coast for a few seconds, I feel the brakes being applied, which screws up a smooth approach to stopped traffic, or even lights. Is there a way to disable this feature?
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      07-02-2014, 04:07 PM   #2
EpistemicConfusion
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I can only think of 2 things that "brake assist" could refer to.

The first doesn't apply to the situation you are describing, but is a safety feature where the car notices you panic braking and "assists" by braking more. This avoids the common problem in emergencies where drivers under brake.

The second is, to quote BMW's website:
Quote:
Originally Posted by http://www.bmw.com/com/en/newvehicles/x/x1/2012/showroom/efficiency/brake_energy_regeneration.html#t=l
Brake Energy Regeneration.

Until now, braking meant energy loss. Brake Energy Regeneration puts an end to this by regaining energy during braking to charge the battery.

As soon as you release the accelerator or apply the brake, the generator is engaged and converts excess kinetic energy into electrical energy. Once the battery is fully charged, the generator is disengaged from the engine. This decreases the load on the engine, reduces emissions and saves fuel. The targeted generation of electrical energy also has another advantage: At full acceleration, the engine also has the propulsive force at its disposal that would otherwise be channelled off to charge the battery in conventional systems. The result is an increase in both cost-efficiency and driving fun.
This does not use the brakes, and I do not know of any way to disable it. I'm thinking something may be wrong if it is noticeable. Does driving in sport or manual mode eliminate the problem?
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      07-02-2014, 05:51 PM   #3
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I usually drive moderately easy, and I tried sport mode, which holds the trans in lower gears, longer, and that was uncomfortable when driving easy. My issue sure feels like braking. I haven't tried manual mode, but I'd rather not have to shift, in normal driving. If this is regen-braking, it's far from unnoticeable. In fact, it's a real drag...

Just thought... wouldn't there have to be a clutch in the alternator? The pulley's gonna turn, whatever the computer says.
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      07-02-2014, 07:27 PM   #4
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I think what you feel is engine breaking. In auto mode the transmission is gearing down to be ready in case you want to speed up again.
You can test this by coasting in M8 vs auto.
This car does not coast well. This is partly why fuel consumption kind of sucks in auto.
PS. I get at least 4 mpg more if I drive in manual mode. I drove a whole tank in manual mode to compare.

Last edited by Njerts; 07-02-2014 at 08:54 PM..
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      07-03-2014, 01:54 PM   #5
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Thanks. Good to know. Might be tunable?

Just thought. We have different transmissions. And it really feels like a drag; either brakes, or added load. The engine doesn't raise revs like it's downshifting.
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      07-03-2014, 04:17 PM   #6
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Brake assist is a safety system that only gets used on very rare occasions. It's not something you will notice on a daily basis. It can sense when someone is trying to press the brake in a hurry/panic stop situation, and it then automatically applies full force to the brakes.
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      07-03-2014, 06:28 PM   #7
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I sit corrected. Hats off to Njerts. The car is shifting down (during a coast) enough to act like engine braking. I don't drive too many A/Ts, but this is my first one to do this. Just a little German to get used to; no biggie.
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      07-05-2014, 11:59 AM   #8
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Quote:
Originally Posted by EpistemicConfusion View Post
I can only think of 2 things that "brake assist" could refer to.

The first doesn't apply to the situation you are describing, but is a safety feature where the car notices you panic braking and "assists" by braking more. This avoids the common problem in emergencies where drivers under brake.

The second is, to quote BMW's website:


This does not use the brakes, and I do not know of any way to disable it. I'm thinking something may be wrong if it is noticeable. Does driving in sport or manual mode eliminate the problem?
The second thing you mentioned is the alternator being engaged. You would not feel the alternator being engaged as it uses the engine and does not affect your speed. The alternator disengagement is used so when you press the throttle, you do not waste any horsepower on the alternator, thus creating a better hp at the wheels. When companies list hp, it is usually listed at the crank, but energy is lost through the alternator, cooling fan, gear case, transfer case etc. BMW designed the alternator with a clutch to disengage when applying throttle. The cooling fan has its own electric motor so that it doesn't take away hp.

I agree with others stating that the transmission shifting down naturally slows the car.
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      07-05-2014, 08:57 PM   #9
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Brake Regeneration

I didn't see anything here that answered the question.

I think BMW's marketing is a little off.

They show a photo of brake caliper, and talk about brake regeneration which is not how it works.

The alternator doesn't charge when you apply power or battery is charged.

The alternator charges when slowing down or all the time on cruise if battery is low.

I can see that also on my scangauge II whichs teaches you to conserve your electricity from battery.

If i drive around town every 2 days, the battery charge will go up to 14.7 volts all the time.

I can go on a day road trip and it takes about 500 miles to fully charge battery back to 12.8 at cruise or decealeration.

Battery voltage state of charge is gas one way or another, and the brake assist is actually charging assist.

Last edited by 0w40X1; 07-05-2014 at 09:37 PM..
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      07-07-2014, 02:11 PM   #10
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The primary question was answered to my satisfaction. At speeds around 45 and below, the transmission downshifts, when the throttle is closed, and this results in a "drag" on the car, similar to the brakes being lightly applied. I've confirmed this myself by watching the tach.
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      07-14-2014, 01:31 PM   #11
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Quote:
Originally Posted by zeevette View Post
I usually drive moderately easy, and I tried sport mode, which holds the trans in lower gears, longer, and that was uncomfortable when driving easy. My issue sure feels like braking. I haven't tried manual mode, but I'd rather not have to shift, in normal driving. If this is regen-braking, it's far from unnoticeable. In fact, it's a real drag
As you have found out from others it sounds like you are experiencing engine braking. If you've driven a manual it's the same thing.

The idea is it helps to regulate speed in a controlled way using the engine resistance rather than additional tyre resistance - as such, it's useful for slowing in slippery surfaces or for longer descents.

The higher the gear the more pronounced it will be.

BMW auto boxes (or rather the ones they, and other German manufacturers, use) are quite advanced and have featured this for many years in varying forms.

If your X1 is similar to mine, when in Sport the braking effect is more pronounced and applies I believe up to third gear.

It makes stop/start driving harsh but is useful for acceleration or for very relaxed smooth driving using the engine instead of braking all the time when going between corners.

If you find it harsh, leave the car in normal rather than sport. it still applies in 1st but is much reduced/off in the other gears

From memory, this is explained in the manual somewhere and it also includes the gears it applies to in each mode.
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