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      06-10-2007, 03:21 PM   #23
lucid
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Originally Posted by southlight View Post
No, it's the engine that produces the power on the BMW system.

Best regards, south
The only way the engine can generate electric power to charge the battery is via the alternator. Is that what you are suggesting? If it is, there is nothing special about that. All IC engine cars have alternators that do exactly that. Unless, they have done something funny with the alternator so that it engages more during braking or something?
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      06-10-2007, 03:43 PM   #24
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Quote:
Originally Posted by lucid View Post
The only way the engine can generate electric power to charge the battery is via the alternator. Is that what you are suggesting? If it is, there is nothing special about that. All IC engine cars have alternators that do exactly that. Unless, they have done something funny with the alternator so that it engages more during braking or something?
Yeah, that's how it works. I think "only" specialty is the ability for the alternator to be totally uncoupled.

As far as the MPG discussion goes. BER saves about 0,3 liter per 100km.

Best regards, south

EDIT:
See how the M5 manages that point:
The electronic throttle valve control is based on a so-called power and torque structure which uses a potentiometer on the accelerator pedal to measure the driver’s wish for power and performance and converts this to the desired function. The power and torque manager adjusts this request function by adding the power signals from the auxiliary engine units, such as the conditioning compressor or the generator.

Based on that you can see the difference:
Let's say you're halfway on the pedal (50%). On the M5 the engine management adds the demand of the alternator which results in e.g. 55%.
On the M3 it stays at 50% and the alternator is uncoupled. Based on that difference there is a slightly better mileage.

Last edited by southlight; 06-10-2007 at 04:08 PM.
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      06-10-2007, 04:37 PM   #25
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Quote:
Originally Posted by southlight View Post
No, it's the engine that produces the power on the BMW system.
Then it's not the same type "regenerative" system that hybirds use, as I suspected. The forward momentum of the car is being turned into energy without the use of fuel soley because the wheels are turning the engine and therefore the alternator during deceleration . It's somewhat of a misnomer because braking really has nothing to do with it.
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      06-11-2007, 03:38 AM   #26
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Originally Posted by GregW / Oregon View Post
Then it's not the same type "regenerative" system that hybirds use, as I suspected. The forward momentum of the car is being turned into energy without the use of fuel soley because the wheels are turning the engine and therefore the alternator during deceleration . It's somewhat of a misnomer because braking really has nothing to do with it.
Right, so it seems not to be a "brake energy" regeneration, it's more of a energy regeneration while braking...

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      06-11-2007, 03:53 AM   #27
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Originally Posted by GregW / Oregon View Post
Then it's not the same type "regenerative" system that hybirds use, as I suspected. The forward momentum of the car is being turned into energy without the use of fuel soley because the wheels are turning the engine and therefore the alternator during deceleration . It's somewhat of a misnomer because braking really has nothing to do with it.
This is a stretch, but as an intellectual exercise: the main alternator is a "load" in the system, and opposes crankshaft motion slightly. So, if you're in gear while decelerating, the alternator opposes the motion of the car, and would have some kind of small effect on slowing the car down. If one could find a way of increasing the load the alternator produces only while braking, the effect would be amplified. But regular alternators are not designed to that, and their belt connection to the shaft is fragile. If that connection was stronger, and if the alternator load could be increased at will, it would be more like the regenerative system in the hybrids, but the engine would definetely not feel smooth when breaking, so probably a bad idea...Also, what would you do with all that extra current generated by the alternator, which would require a bank of batteries to store...
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      06-11-2007, 05:41 AM   #28
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Quote:
Originally Posted by lucid View Post
This is a stretch, but as an intellectual exercise: the main alternator is a "load" in the system, and opposes crankshaft motion slightly. So, if you're in gear while decelerating, the alternator opposes the motion of the car, and would have some kind of small effect on slowing the car down. If one could find a way of increasing the load the alternator produces only while braking, the effect would be amplified. But regular alternators are not designed to that, and their belt connection to the shaft is fragile. If that connection was stronger, and if the alternator load could be increased at will, it would be more like the regenerative system in the hybrids, but the engine would definetely not feel smooth when breaking, so probably a bad idea...Also, what would you do with all that extra current generated by the alternator, which would require a bank of batteries to store...
To add to this, the additional load on the crankshaft would be proportional to the current flowing in the alternator, so it would be possible to manage this load electronically to give smooth braking (though I don't know how BMW has actually implemented it).

A properly implemented system would to some extent improve fuel economy and power as well as conserving brake pads. Someone would need to do the calculation to determine whether these effects would be measurable or it is just marketing guff
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      06-11-2007, 01:58 PM   #29
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To add to this, the additional load on the crankshaft would be proportional to the current flowing in the alternator, so it would be possible to manage this load electronically to give smooth braking (though I don't know how BMW has actually implemented it).

A properly implemented system would to some extent improve fuel economy and power as well as conserving brake pads. Someone would need to do the calculation to determine whether these effects would be measurable or it is just marketing guff
Agreed. I am wondering if designing such an alternator would be tricky though. Any electrical engineers reading this?
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      06-11-2007, 04:09 PM   #30
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ahhh snap i just caught this look down in the the little brown brief description on the right.. its says

22.8mpg!

LOOKS LIKE WE ARE WORRYING FOR NOTHING..HAHA

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      06-11-2007, 05:42 PM   #31
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ahhh snap i just caught this look down in the the little brown brief description on the right.. its says

22.8mpg!

LOOKS LIKE WE ARE WORRYING FOR NOTHING..HAHA
NOT US SPEC!!!

People keep getting that confused.
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      06-11-2007, 06:26 PM   #32
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Quote:
Originally Posted by Boostedg35 View Post
ahhh snap i just caught this look down in the the little brown brief description on the right.. its says

22.8mpg!

LOOKS LIKE WE ARE WORRYING FOR NOTHING..HAHA
Two problems with that assumption.
1) As Epacy says, testing was not done to US EPA standards.
2) Gallons may be in imperial measure (UK gallon = 1.2 US gallons), since this was in a UK mag.
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      06-11-2007, 06:56 PM   #33
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2) Gallons may be in imperial measure (UK gallon = 1.2 US gallons), since this was in a UK mag.
so that makes it 19!
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      06-11-2007, 07:55 PM   #34
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so that makes it 19!

Number-crunching wise......yes.

I don't think that method is reliable either.
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      06-11-2007, 09:10 PM   #35
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I had a e39 V8 M5, never have I seen 22.8mpg.

.... thats what I get now with a I6-e90/325
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