BMW's engine autostop feature

I've had the experience of driving a BMW X1 this week, as a loaner car.
My own car was in the body shop for some damages, so the insurance
company sprang for the X1 as my loaner. I was taken a little off-guard
by the engine auto-stop feature when you come to an idling situation,
like stoplights, parking, etc. I eventually got used to it, and actually
think it may have helped save a lot of gas for me, as I am mostly doing
city driving. But even though I liked saving the gas, it seems to me
that this would be hard on the batteries, as I noticed that all of the
lights and AC remain open during this time. My question is, how does BMW
achieve this? Does it have some special batteries, or are they just the
conventional lead-acid's?

Yousuf Khan

On 11/04/2013 06:18, Yousuf Khan wrote:
> I've had the experience of driving a BMW X1 this week, as a loaner car.
> My own car was in the body shop for some damages, so the insurance
> company sprang for the X1 as my loaner. I was taken a little off-guard
> by the engine auto-stop feature when you come to an idling situation,
> like stoplights, parking, etc. I eventually got used to it, and actually
> think it may have helped save a lot of gas for me, as I am mostly doing
> city driving. But even though I liked saving the gas, it seems to me
> that this would be hard on the batteries, as I noticed that all of the
> lights and AC remain open during this time. My question is, how does BMW
> achieve this? Does it have some special batteries, or are they just the
> conventional lead-acid's?
>

Heavy duty batteries, combined with regenerative brakes in my car
(Mini). Mine's 60,000 miles/5 years and still going.

I have read that the system is only of benefit if the stop period is
above a certain time. There's some research out there somewhere - 30s
and up ISTR.

Rob

On 11/04/2013 08:47, RJH wrote:
> On 11/04/2013 06:18, Yousuf Khan wrote:
>> I've had the experience of driving a BMW X1 this week, as a loaner car.
>> My own car was in the body shop for some damages, so the insurance
>> company sprang for the X1 as my loaner. I was taken a little off-guard
>> by the engine auto-stop feature when you come to an idling situation,
>> like stoplights, parking, etc. I eventually got used to it, and actually
>> think it may have helped save a lot of gas for me, as I am mostly doing
>> city driving. But even though I liked saving the gas, it seems to me
>> that this would be hard on the batteries, as I noticed that all of the
>> lights and AC remain open during this time. My question is, how does BMW
>> achieve this? Does it have some special batteries, or are they just the
>> conventional lead-acid's?
>>
>
> Heavy duty batteries, combined with regenerative brakes in my car
> (Mini). Mine's 60,000 miles/5 years and still going.
>
> I have read that the system is only of benefit if the stop period is
> above a certain time. There's some research out there somewhere - 30s
> and up ISTR.
>
> Rob
>

Actually, nothing like the regenerative braking as utilised by electric
vehicles, it is just "Intelligent Alternator Control". All this does is
turn on the alternator during "over-run" or whilst braking, instead of
charging all the time.
It can be disconcerting to watch the battery voltage fall below 11.8
volts on a longer run, such as on the motorway using cruise control, but
this can be counteracted by turning on the side-lights, which then
maintains 13+ volts across the system.
The stop/start system only functions when the battery has enough charge,
the engine is warm and the Air/ Con is not on.
Initially, this was only with 4 pot manual cars, recently rolled out
across the ranges.

The batteries are known as Absorbant Glass Mat, still lead acid, but
these are now known to not be the optimum chemistry for this system.
There are many cases of the batteries not lasting for more than three
years in certain circumstances.

There is research into carbon / lead acid chemistry for the battery.

David

On 11/04/2013 08:47, RJH wrote:
> On 11/04/2013 06:18, Yousuf Khan wrote:
>> I've had the experience of driving a BMW X1 this week, as a loaner car.
>> My own car was in the body shop for some damages, so the insurance
>> company sprang for the X1 as my loaner. I was taken a little off-guard
>> by the engine auto-stop feature when you come to an idling situation,
>> like stoplights, parking, etc. I eventually got used to it, and actually
>> think it may have helped save a lot of gas for me, as I am mostly doing
>> city driving. But even though I liked saving the gas, it seems to me
>> that this would be hard on the batteries, as I noticed that all of the
>> lights and AC remain open during this time. My question is, how does BMW
>> achieve this? Does it have some special batteries, or are they just the
>> conventional lead-acid's?
>>
>
> Heavy duty batteries, combined with regenerative brakes in my car
> (Mini). Mine's 60,000 miles/5 years and still going.
>
> I have read that the system is only of benefit if the stop period is
> above a certain time. There's some research out there somewhere - 30s
> and up ISTR.
>
> Rob
>

Forgot to mention, BMW now state that fuel can be saved even with only a
4 second engine off period.

David

On 11/04/2013 8:25 AM, David wrote:
> Actually, nothing like the regenerative braking as utilised by electric
> vehicles, it is just "Intelligent Alternator Control". All this does is
> turn on the alternator during "over-run" or whilst braking, instead of
> charging all the time.

So does the alternator somehow produce a braking force on the engine
during this condition?

> It can be disconcerting to watch the battery voltage fall below 11.8
> volts on a longer run, such as on the motorway using cruise control, but
> this can be counteracted by turning on the side-lights, which then
> maintains 13+ volts across the system.

I haven't noticed the voltage gauge yet, but I don't think I'll have
this problem anyway, since I'm in Canada and we have daytime running
lights up here. So it'll be producing a constant drain on the electrical
system all of the time anyway.

> The stop/start system only functions when the battery has enough charge,
> the engine is warm and the Air/ Con is not on.

Actually, I found it was still working while the AC was on. At least the
AC light was on when I looked at it.

However, today, it suddenly got colder again, hovering around 0C, it's
going to snow heavily later tonight, so I noticed that it's
automatically disabled the auto-stop feature. I think the manual
mentioned that it disables the feature during outside temperatures of
less than 37F/3C.

> The batteries are known as Absorbant Glass Mat, still lead acid, but
> these are now known to not be the optimum chemistry for this system.
> There are many cases of the batteries not lasting for more than three
> years in certain circumstances.
>
> There is research into carbon / lead acid chemistry for the battery.

It starts up extremely quickly too, just let go of the brakes and it
automatically starts with barely any delay.

Yousuf Khan

On 11/04/2013 10:03 AM, David wrote:
> Forgot to mention, BMW now state that fuel can be saved even with only a
> 4 second engine off period.

Yes, read that in the manual.

Yousuf Khan

On 11/04/2013 19:22, Yousuf Khan wrote:
> On 11/04/2013 8:25 AM, David wrote:
>> Actually, nothing like the regenerative braking as utilised by electric
>> vehicles, it is just "Intelligent Alternator Control". All this does is
>> turn on the alternator during "over-run" or whilst braking, instead of
>> charging all the time.
>
> So does the alternator somehow produce a braking force on the engine
> during this condition?

It can be felt as a minor deceleration. A bit more than engine braking
The alternator is not turned on instantly, but softly over a period of a
few seconds. You wouldn't want a jolt that would strain the belt and
other mounts if it suddenly came on.

>
>> It can be disconcerting to watch the battery voltage fall below 11.8
>> volts on a longer run, such as on the motorway using cruise control, but
>> this can be counteracted by turning on the side-lights, which then
>> maintains 13+ volts across the system.
>
> I haven't noticed the voltage gauge yet, but I don't think I'll have
> this problem anyway, since I'm in Canada and we have daytime running
> lights up here. So it'll be producing a constant drain on the electrical
> system all of the time anyway.

There isn't as such a voltmeter on the car. The main ECU voltage can be
brought up into one of the displays, if you know how to ...


>
>> The stop/start system only functions when the battery has enough charge,
>> the engine is warm and the Air/ Con is not on.
>
> Actually, I found it was still working while the AC was on. At least the
> AC light was on when I looked at it.

The engine drives the A/C compressor, so if the engine is not running,
then the A/C compressor will not run. There are some variables as to
whether the A/C operates with regard to outside temperature, internal
temp, humidity and 'misting' of the screens et cetera. There may be
different programs in different countries.

The latest BMW I have, a 2011 120i, has a different 'Auto' program to
the six BMWs I had before it.

>
> However, today, it suddenly got colder again, hovering around 0C, it's
> going to snow heavily later tonight, so I noticed that it's
> automatically disabled the auto-stop feature. I think the manual
> mentioned that it disables the feature during outside temperatures of
> less than 37F/3C.
>
>> The batteries are known as Absorbant Glass Mat, still lead acid, but
>> these are now known to not be the optimum chemistry for this system.
>> There are many cases of the batteries not lasting for more than three
>> years in certain circumstances.
>>
>> There is research into carbon / lead acid chemistry for the battery.
>
> It starts up extremely quickly too, just let go of the brakes and it
> automatically starts with barely any delay.
>
> Yousuf Khan

Over this this of the pond, Stop/Start would initially only work if the
transmission was taken out of gear (remember at first it was on manual
shifters only) and the handbrake applied.
This may have changed on the very latest cars.

David

On 12/04/2013 9:06 AM, David wrote:
> On 11/04/2013 19:22, Yousuf Khan wrote:
>> So does the alternator somehow produce a braking force on the engine
>> during this condition?
>
> It can be felt as a minor deceleration. A bit more than engine braking
> The alternator is not turned on instantly, but softly over a period of a
> few seconds. You wouldn't want a jolt that would strain the belt and
> other mounts if it suddenly came on.

Now, this is a little strange to me, it was my understanding that the
alternator is always on, while the engine is running, so that all
electrical activity is run through the alternator, including basics such
as ignition through to optionals like lighting and entertainment.
Including the recharging of the battery. Are you saying that the
alternator is not always being used?

> There isn't as such a voltmeter on the car. The main ECU voltage can be
> brought up into one of the displays, if you know how to ...

Ok, insider knowledge.

>>> The stop/start system only functions when the battery has enough charge,
>>> the engine is warm and the Air/ Con is not on.
>>
>> Actually, I found it was still working while the AC was on. At least the
>> AC light was on when I looked at it.
>
> The engine drives the A/C compressor, so if the engine is not running,
> then the A/C compressor will not run. There are some variables as to
> whether the A/C operates with regard to outside temperature, internal
> temp, humidity and 'misting' of the screens et cetera. There may be
> different programs in different countries.
>
> The latest BMW I have, a 2011 120i, has a different 'Auto' program to
> the six BMWs I had before it.

Here in Canada, you can get every climate test available to you within a
matter of days, if not hours. A couple of days ago, it was a mild 15C
outside. Yesterday, it hovered up and down around 0-5C, and clear.
Today, it was below 0C and there was a snowstorm! (How's that for Global
Warming?)

During the mild days, the auto-stop worked consistently.

Yesterday, when bouncing between 0-5C, especially once the temperature
fell to 3C, you'd hear warning sound inside the car about cold temps,
and it would automatically disable auto-stop. You'd see throughout the
day while driving when auto-stop was working if it was above 3C, but
then disabled again at 3C. As I said, in Canada you get to see in front
of your eyes how the computer adjusts to its environmental parameters.

Today, with the snowstorm, I also got the chance to see how the Xdrive
AWD system works, and compare it to my Subaru.

>> It starts up extremely quickly too, just let go of the brakes and it
>> automatically starts with barely any delay.
>>
>> Yousuf Khan
>
> Over this this of the pond, Stop/Start would initially only work if the
> transmission was taken out of gear (remember at first it was on manual
> shifters only) and the handbrake applied.
> This may have changed on the very latest cars.

Yeah, this one was on an automatic transmission car, and it goes well
beyond just auto-stopping for parking. I read in the manual that it'll
go into auto-stop when you've come to a full stop for at least 1 second,
as long as you've got the transmission in regular Drive (D) mode, and
not in Drive Sport (DS) mode, or manual mode. Also if you've got your
steering turned steeply, then it won't go into auto-stop: if your
steering is cranked like that, then it determines that you're trying to
make a turn at that moment, making it dangerous to auto-stop. And of
course as mentioned before, it'll determine the temperature outside and
decide whether to activate auto-stop or not too.

Anyways, I picked my own car (a Subaru) back up today, and gave the BMW
loaner back, so it was fun getting to know it. Some features I liked
about it (like this one), others that I didn't.

Yousuf Khan

"Yousuf Khan" > wrote in message
...
> On 12/04/2013 9:06 AM, David wrote:
>> On 11/04/2013 19:22, Yousuf Khan wrote:
>>> So does the alternator somehow produce a braking force on the engine
>>> during this condition?
>>
>> It can be felt as a minor deceleration. A bit more than engine braking
>> The alternator is not turned on instantly, but softly over a period of a
>> few seconds. You wouldn't want a jolt that would strain the belt and
>> other mounts if it suddenly came on.
>
> Now, this is a little strange to me, it was my understanding that the
> alternator is always on, while the engine is running, so that all
> electrical activity is run through the alternator, including basics such
> as ignition through to optionals like lighting and entertainment.
> Including the recharging of the battery. Are you saying that the
> alternator is not always being used?

Indeed he is.

This is a good feature - less strain on the alternator, very slightly
greater deceleration on over-run and less power drained during acceleration,
although IIRC, even in a 7 series it only takes about 1kW.

>
>> There isn't as such a voltmeter on the car. The main ECU voltage can be
>> brought up into one of the displays, if you know how to ...
>
> Ok, insider knowledge.
>
>>>> The stop/start system only functions when the battery has enough
>>>> charge,
>>>> the engine is warm and the Air/ Con is not on.
>>>
>>> Actually, I found it was still working while the AC was on. At least the
>>> AC light was on when I looked at it.

If it is very cold the AC does not actually run.

>>
>> The engine drives the A/C compressor, so if the engine is not running,
>> then the A/C compressor will not run. There are some variables as to
>> whether the A/C operates with regard to outside temperature, internal
>> temp, humidity and 'misting' of the screens et cetera. There may be
>> different programs in different countries.
>>
>> The latest BMW I have, a 2011 120i, has a different 'Auto' program to
>> the six BMWs I had before it.
>
> Here in Canada, you can get every climate test available to you within a
> matter of days, if not hours. A couple of days ago, it was a mild 15C
> outside. Yesterday, it hovered up and down around 0-5C, and clear. Today,
> it was below 0C and there was a snowstorm! (How's that for Global
> Warming?)
>
> During the mild days, the auto-stop worked consistently.
>
> Yesterday, when bouncing between 0-5C, especially once the temperature
> fell to 3C, you'd hear warning sound inside the car about cold temps, and
> it would automatically disable auto-stop. You'd see throughout the day
> while driving when auto-stop was working if it was above 3C, but then
> disabled again at 3C. As I said, in Canada you get to see in front of your
> eyes how the computer adjusts to its environmental parameters.
>
> Today, with the snowstorm, I also got the chance to see how the Xdrive AWD
> system works, and compare it to my Subaru.
>
>>> It starts up extremely quickly too, just let go of the brakes and it
>>> automatically starts with barely any delay.
>>>
>>> Yousuf Khan
>>
>> Over this this of the pond, Stop/Start would initially only work if the
>> transmission was taken out of gear (remember at first it was on manual
>> shifters only) and the handbrake applied.
>> This may have changed on the very latest cars.
>
> Yeah, this one was on an automatic transmission car, and it goes well
> beyond just auto-stopping for parking. I read in the manual that it'll go
> into auto-stop when you've come to a full stop for at least 1 second, as
> long as you've got the transmission in regular Drive (D) mode, and not in
> Drive Sport (DS) mode, or manual mode. Also if you've got your steering
> turned steeply, then it won't go into auto-stop: if your steering is
> cranked like that, then it determines that you're trying to make a turn at
> that moment, making it dangerous to auto-stop. And of course as mentioned
> before, it'll determine the temperature outside and decide whether to
> activate auto-stop or not too.
>
> Anyways, I picked my own car (a Subaru) back up today, and gave the BMW
> loaner back, so it was fun getting to know it. Some features I liked about
> it (like this one), others that I didn't.
>
> Yousuf Khan

On 13/04/2013 12:25 PM, R. Mark Clayton wrote:
> "Yousuf Khan" > wrote in message
> ...
>> Now, this is a little strange to me, it was my understanding that the
>> alternator is always on, while the engine is running, so that all
>> electrical activity is run through the alternator, including basics such
>> as ignition through to optionals like lighting and entertainment.
>> Including the recharging of the battery. Are you saying that the
>> alternator is not always being used?
>
> Indeed he is.
>
> This is a good feature - less strain on the alternator, very slightly
> greater deceleration on over-run and less power drained during acceleration,
> although IIRC, even in a 7 series it only takes about 1kW.

So while the alternator is not running, is it running back on the
batteries again?

>>>> Actually, I found it was still working while the AC was on. At least the
>>>> AC light was on when I looked at it.
>
> If it is very cold the AC does not actually run.

Well, it's not running to the extent that's it being used to cool the
environment inside the cabin, but I know that most cars use the AC to
create de-humidified air to blow through the windscreen to defog it.

Yousuf Khan