BMW's "Brake Energy Regeneration" technology
Autospies says that they've gotten their hands on the first picture of "BMW regenerative brake technology in action on a USA model" (a 550i GT). Well, we're interested in the technology, but something about the Celsius temperature gauge and the kilometer label tells us that maybe this is a Eurospec dash. Whatever the case, one nifty feature of the way BMW's system works is that the alternator disengages until the vehicle slows down. This way, efficiency is increased because the freewheeling alternator doesn't draw power when it's not needed. An Absorption Glass Mat (AGM) battery helps provide power when needed if the car isn't slowing down. You can learn more about the system here. Thanks to Agent001 for the tip!
[Source: AutoSpies]
Reader Comments (Page 1 of 1)
why not the LS2LS7? 8:15PM (5/21/2009)
Batteries don't produce power, they just store it. If the alternator really cuts out for any significant amount of time, the computer will surely just turn it back on long enough to recharge the battery.
In city traffic, it's possible all your electric power could come from "free energy" (i.e. only turning on the alternator while decelerating.
Even a 100A alternator (1300W) is only using up about 2HP, so don't expect fuel economy miracles.
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Mark 10:02PM (5/21/2009)
The author has this wrong. The alternator ENGAGES during deceleration in order to store energy to the battery. There must also be some battery management in order to make sure the battery is not completely full during the braking cycle and that is why the alternator can shut off during cruise. It is turned off during acceleration in order to increase performance.
The 'miracle' here is that it's a very simple way to increase efficiency just a little bit.
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Chris M 11:15PM (5/21/2009)
It is such a simple idea that one wonders why it wasn't introduced earlier. I suspect the reason is the sophisticated type of controls necessary to make it work right are relatively recent developments.
The "absorbed glass mat" batteries are merely sophisticated lead acid batteries, the electrolyte is "absorbed" into a fiberglass mat between the cathode and anode, that makes them darn near spillproof.
lne937s 12:10PM (5/22/2009)
I was going to try something like this a couple of years ago, but never got around to it...
My idea was to take the voltage regulator and do a few mods. With a couple of resistor changes, you can change the reference voltage. Changing the reference voltage changes the voltage sent to the field coil in the alternator. If the battery voltage is higher than the reference voltage, the alternator free-wheels. By using a relay coupled to the brake light circuit, you could switch reference voltages every time you applied the brakes. I was thinking about switching between ~13v and ~15v (a 12v system is typically 14.4 volts). ~15v would charge the battery and ~13v would engage the alternator once the battery discharges (makes the voltage drop) to keep it from going dead if you didn't use the brakes for a while. There are some heavy-duty external voltage regulators (not that it is a hard circuit to build) available that use variable resistors to allow you to change voltages in the car while in use- by using 2 variable resistors with a relay switching between them, you could play around until you found the right mix. Coupled with a good battery and a few farads of supercaps (I was going to use Maxwell)...
The idea is so simple, anybody could do it. Once the bugs are figured out, it wouldn't cost more than a couple hundred dollars to make, with the vast majority of that being the capacitors. A milder version without the caps would cost the price of a couple of resistors and a relay. However, getting it right would take some tweaking (and maybe a few spare batteries and alternators). If only I had the time...
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Andy 1:48PM (5/22/2009)
I wish someone would do something similar with the air conditioner compressor. It's not needed all the time. It should disengage when accelerating or power is needed and engage during deceleration. A/C causes a substantial hit in performance.
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Noz 4:25PM (5/22/2009)
All this effort from BMW when all they had to do was lighten up their cars, make more efficiently designed frames, and use smaller, more efficient engines.
Typical Germanic approach...make everything complicated beyond logic.
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