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BMW Introduces Intelligent Alternator Control with Regenerative Braking; Reduces Fuel Consumption by About 4%

29 September 2006

At the Paris Auto Show, BMW introduced a system it calls Intelligent Alternator Control (IAC) to generate electric power for a car’s on-board network exclusively in overrun and during braking—IAC thus also incorporates a system for regenerating brake energy.

The system is part of a larger BMW initiative to improve the overall efficiency of a vehicle by decreasing ancillary loads on the engine and recuperating more of the waste heat energy. (BMW is currently involved in one of several projects tackling the development of a thermoelectric waste heat recovery system targeted to deliver a 10% improvement in fuel economy. More on this below.)

Only about 25–30% of the energy contained in fuel is actually used for driving the vehicle. Most of the energy consumed is still converted into heat, although the fuel burnt also serves to generate electrical energy for the on-board network.

Electric power requirements for mid-size and luxury cars. Source: DOE

The on-board demand for power is also steadily increasing, even without factoring in traction support. Air conditioning, telecommunications, entertainment, as well as new components for enhanced safety and driving dynamics such as suspension management, Active Steering, engine management, and ABS all require electric power.

A mid-size car currently has an electric power requirement of about 3.5kW for all its systems. (See chart at right.) Hence, the generation of electricity for the car’s on-board network consumes an increasing share of the power generated by the engine.

With the IAC system, the alternator will operate primarily when the engine has no need for power—i.e., in overrun or during braking. The alternator remains passive while the car is under power, with needed electrical power provided by the battery.

The alternator becomes active when the engine switches to overrun or if the battery charge is insufficient.

For regenerative braking, a power converter fitted directly within the brake system converts the energy generated upon application of the brakes into electric power.

The battery is charged to only about 80% of its capacity whenever the engine is pulling the vehicle, always maintaining an adequate reserve for the consumption of energy at a standstill and for starting the vehicle. A higher charge level is generated only when the vehicle is in overrun or upon application of the brakes, that is in phases with a better energy balance.

With the number of charge cycles increasing thanks to these specific control functions, BMW combines Intelligent Alternator Control with AGM (absorbant glass mat) batteries able to handle a higher load than conventional lead/acid batteries.

BMW found that the on-demand generation of electrical energy helps to reduce fuel consumption in the EU homologation test by approximately 4%. The driver also has access to more engine power for acceleration and dynamic driving.

BMW’s electric water pump.

IAC is one effort to generate electrical energy in the car more efficiently, and use that energy for a wider range of purposes and functions. BMW is now using new electrical coolant pumps in its straight-six engines. The electrical pumps operating exactly—and only—when required, meaning that they develop their maximum output and performance only at high and very high speeds.

They remain passive immediately after the engine has been started, ensuring in this way that the engine is warmed up more quickly. This alone helps to reduce fuel consumption in the EU homologation test by approximately 2%.

The waste heat recovery project envisions a heat exchanger in the exhaust line (middle of car) that then feeds a working fluid to the thermoelectric generator (TGM). Click to enlarge.

Thermoelectric Waste Heat Recovery. BMW is a member of one of four teams engaged in a DOE-sponsored project on thermoelectric waste heat recovery. (Earlier post.) BMW’s team is lead by BSST, with Visteon, Marlow, Purdue, UC Santa Cruz, NREL, Teledyne and JPL also as contributors.

Another team is lead by GM and GE, with University of Michigan, University of South Florida, Oak Ridge National Laboratory, and RTI International as members.

The BMW team is using a 2006 BMW 530i as the target platform. The 3.0-liter engine is of the newest BMW generation, with characteristics representative of engines in the 2010 to 2015 timeframe.

The project, which began in 2005, has four phases. The teams are now in phase 2, in which they are building the subsystem elements, testing them independently, and then updating their system model.

Next year will see the integration and operation of the components as a system. Subsequent to that will be vehicle integration and testing at NREL.


September 29, 2006 in Fuel Efficiency, Thermoelectrics, Vehicle Systems | Permalink | Comments (26) | TrackBack (0)


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By 2010 BMW may have a vehicle that resembles a 1st generation Prius

I have mixed feelings about this kind of project.

On one hand, I applaud any effort to reduce fossil fuel consumption, whether that's conservation, more efficient cars, shifting transportation away from oil, etc.

But the feels to me like BMW is spending a lot of money to make the most efficient, highest tech buggy whip on the planet.

If nothing else it should be fairly easy to spread the technology out throughout most of their lineup.

This an attempt at creating a mild gas-electric hybrid without BMW directly stating so. Perhaps Europeans are not ready to publicly admit the advantage of the Hybrids. By not having the alternator taking away engine power during acceleration, it kinda getting close to getting a boost by the motor/generator in Honda's IMA (Integrated Motor Assist) scheme. And of course, regenerative braking is smackdab hybrid kinda thing.

Did someone compare a BMW to a Toyota Prius? Really?

Regardless, BWM's efforts on capturing the wasted heat will prove far more beneficial than hybrid tehcnology, to people who log mostly highway miles. Not everyone is stuck in the opening scene to the movie, Office Space (apologies for the somewhat obscure reference)!

Down the road, it would make sense for these technologies to converge. With hybrid technologies moving along, I am happy to see some other companies focussing on this. It's a more efficient use of resources overall.

On-demand activation of the alternator should NOT be interpreted as a micro-hybrid solution. There is no indication here that the alternator ever doubles as a starter or assist motor, nor that it is connected to the crankshaft by anything other than a standard belt. BMW is simply optimizing the times at which electricity is generated by using the battery as a buffer. This requires an alternator with a slightly higher power rating, a circuit breaker and some software.

The electrically powered centrifugal water pumps are no longer belt-driven. This means they can be smaller and mounted some distance from the engine. The pump's speed range can be designed and controlled independently of crankshaft speed, greatly improving the device's efficiency. That includes shutting it off altogether during extended idling and initial warm-up, which saves a little fuel. More importantly, it shortens the time intervals during which the exhaust gas aftertreatment is below its light-off temperature (and hence ineffective).

For a gasoline ICE to achieve SULEV emissions in the standardized driving cycle, its three-way catalyst has to be operational within ~20 seconds of a cold start. After that, actual tailpipe emissions are virtually undetectable - the exhaust gas is sometimes actually cleaner than the ambient air! If EPA were to double the length of its driving cycle, all gasoline cars would immediately appear to emit only about half as many toxins per mile.

Both of the innovations discussed above are useful but let's be honest, fairly dull. On the other hand, they are cheap enough to become standard features in the whole product line. Competitors in all markets either have similar solutions or will have them before long.

The *cumulative* effect on e.g. GHG emissions, of a ho-hum 4-5% improvement in fuel economy in millions of vehicles will be far greater than a dramatic 40-50% improvement in just 1% of the LDV market. Perhaps this also highlights a cultural difference between Europeans - whose main concern is not giving anyone a free ride on the environment - and Americans, who seem to prefer quantum leaps in technology that give early adopters bragging rights.

Thin-film thermocouples sound exotic today, but so did jet-guided gasoline direct injection, variable geometry turbochargers and a host of other automotive technologies just a few years ago. They are really just more worthwhile tinkering at the margins of ICE technology, though to be fair, only a few measures have delivered a 10% improvement by themselves. Usually the gains are in the single digits.

Unfortunately, ICE and drivetrain engineers typically see the fruits of all this fuel efficiency labor negated by ever-greater vehicle weight (to meet safety regs and customer demand for comfort and convenience) and an ever-greater excess of available power (so we can be in even more of a hurry all the time). The net result is that fleet average *vehicle* fuel economy has improved at a much slower rate in Europe. In the US, it has even fallen since the early 90s, due to the SUV boom whose true impact is masked by the E85 loophole in CAFE.

Turbine connected generator would be great for reclaiming energy and reducing fuel consumption at highway speeds. Keep the wastegate shut and maximize energy capture to provide more electrical power so less gas power is required (of course this will cause the electrical output to decrease as a function of the amount of exhaust produced so this scheme requires a gasoline engine running atleast a little on the highway). Thermal electric generators used with an oil cooler immediately after the turbo to make use of the heat off of it in addition to other areas to maximize energy reclamation...great stuff until you look at the cost of the implementation.

"Unfortunately, ICE and drivetrain engineers typically see the fruits of all this fuel efficiency labor negated by ever-greater vehicle weight (to meet safety regs and customer demand for comfort and convenience) and an ever-greater excess of available power (so we can be in even more of a hurry all the time). The net result is that fleet average *vehicle* fuel economy has improved at a much slower rate in Europe. In the US, it has even fallen since the early 90s, due to the SUV boom whose true impact is masked by the E85 loophole in CAFE."

Rafael. As usual, you have hit the nail on the head. The faster we run, the farther behind we get. As long as we continue to add more googaws and weight to our vehicles we will never make much progress. And oh yeh. It is critical that we be able to watch DVDs in our vehicles. Can't let those kids be bored for five seconds. Whatever happened to basic transportation? That's why I am happiest when I am getting around on my bicycle.

Just as a side note, Toyota already has in production, an exhaust heat recovery system, and they are working a more comprehensive system.

I'm guessing it's quite flattering to Toyota that so many automakers are now on the hybrid bandwagon, with so many being actively involved in R & D.

But BMW is definitely doing a good thing here, and I rather prefer BMW's direction than the direction Benz is taking with their Bluetec systems.

BMW had the TurboSteamer which added 14hp to a 1.8L engine and reduced fuel consumption 15%. With this and taking accesories off the engine, there might be significant savings in fuel, while boosting performance.

Toyo -

Toyota was not the first to produce hybrid electric cars. That would be the Lohner Porsche of 1900, courtesy of good old Ferdinand. Audi tried again in the 90s with its Duo but the lead-acid battery technology of the day precluded market success.

Toyota decided to build hybrids because fuel economy was a big issue in Japan even in the 1990s and, because a small group of highly respected engineers insisted. However, hybrids remained something of a low-volume science project until the US market opened up. And that happened mostly because CARB, acknowledging after the EV-1 fiasco that BEVs were not yet feasible, decided to rescue its policy by awarding ZEV credits for hybrids (among other alternatives incl. fuel cells). Don't get me wrong, Toyota deserves full credit for sticking with hybrids at a time when everyone else in the industry pooh-poohed the idea. Just don't pretend that it was all divine inspiration.

Also, note that BMW's ideas can be applied to both gasoline and diesel engines. MB's Bluetec technology is designed to allow lean-burn diesels to meet strict US emissions regs. Buying a diesel instead of a gasoline engine would be the single most effective purchasing decision US consumers could take wrt their personal GHG footprint - hybrids are similarly effective only in stop-and-go traffic.

s -

I suspect the turbosteamer science project will never make it into series production if thin-film solid state thermocouples become technologically and economically viable alternatives. High-pressure steam is not something you want in a car, though it might still be of interest for rail applications.

Opinions are like noses...everyone has one. My "nose" tells me that IR semiconductors will become more efficient for recovering heat and making electricity.

"Buying a diesel instead of a gasoline engine would be the single most effective purchasing decision US consumers could take wrt their personal GHG footprint - hybrids are similarly effective only in stop-and-go traffic."

The majority of US transportation is stop-and-go traffic. A PLUG-IN hybrid with cleaner/better regulated power sources is a better option wrt to GHG

"The majority of US transportation is stop-and-go traffic"...

So then why do we all need big ass 3.0 plus engines?

I keep hearing that hybrids are only effective in stop and go traffic and yet my Prius exceeds its rated EPA hwy mpg of 51 mpg on the highway at a steady cruise rate of 65 mph. Maybe I'm just lucky. Maybe I got the Prius that was built differently than the others.

My Prius does fine in stop and go traffic,too, but I find it does better on the highway compared to its EPA numbers.

This is due to a small efficient engine, in addition to great aerodynamics.
Rafael Seidl, SJC,
There is another advantage to utilizing hot post emission control system exhaust. It is the fact that the exhaust gases would be cooler, and if you strip enough energy from it, you may forsake the muffler, or at least shrink it. This might add another 1-3 HP to your car/truck.
_"Unfortunately, ICE and drivetrain engineers typically see the fruits of all this fuel efficiency labor negated by ever-greater vehicle weight (to meet safety regs and customer demand for comfort and convenience) and an ever-greater excess of available power (so we can be in even more of a hurry all the time)."
___Side impact airbags w/ rollover protection, and traction/stability enhancements, would help mitigate/eliminate many crashes/dangerous spinouts. The equipment is light and getting lighter/smaller. That should slow vehicle safety induced weight growth for a while.
_For enhanced all around crash safety, carbon fiber composites wedded to advanced/high grade aluminum alloys and plastic, would be one option. Often small events create localized weaknesses, which also tend to focus forces and moments of the structural member, at the damaged point of the member. This creates a point of concentration for forces during high stress/impact load events (crash). The aluminum/plastic protects the strength of carbon fiber composites, from everyday vibrations/jostling, due to road conditions. They would also protect them from small incidents and dings/dents. _
In future vehicles, it may be possible to be in a light Class B vehicle, have a head-on collision with a 18 wheeler, at a net 100mph/~160kph, and live/walk away (there are many 2 or 4 lane, high speed rural roads that used to service trucks and farmers, but now also service exurb/fringe suburb developments, w/families/commuters).


You've just proved my point that Europeans are not ready to publicly embrace hybrids. There is no sound technical reason to have both a large alternator AND a starter, other than just a deliberate attempt NOT to make a hybrid. Especially when both starter and alternator can be combined into one even larger alternator. More simplification can be done by having the alternator/starter directly driven by the engine, or even better than that, it is incorporated into the engine as the flywheel, like the Honda IMA scheme, thereby saving the weight and cost of the starter motor, gear, and solonoid, AND the weight of the flywheel, AND the weight of belt drive and motor bearing. A larger alternator will give better regenerational braking efficiency and more efficient at boosting the engine torque during acceleration.

Likewise, the value of exhaust heat is not great if one already has a very efficient Atkinson-cycle engine with high expansion ratio, with even further improvement by running in the ultra-lean mode courtesy of Hydrogen injection. So, any effort at exhaust heat recycling must not add much cost nor weight, nor complication to a modern ICE-hybrid car that is already quite complicated.

Roger -

there are hybrid models on the European market, though admittedly few from European brands. The market reception for them has been more modest than in the US, mostly because diesel is a cheaper and available alternative over here. Please bear in mind that consumers here are not required to embrace hybrids just because they're all the rage in California.

It's not that European carmakers don't see the technical merits of hybridization, rather the economics are not sufficiently attractive in the context of the European market. That would change if fuels were taxed according to their energy content.

This is why e.g. Dr. Piech, chairman of VW's board of supervisors, stated in a recent lecture I attended that if it all, European carmakers should focus only on diesel hybrids (as Citroen PSA is doing). He indicated there was no value in chasing after Toyota with a me-too gasoline-based solution given the commanding technology lead and deep pockets of the hybrid market leader.

Note that VW's Lupo subcompact was equipped with a three-cylinder diesel engine and a stop-start microhybrid system. In spite of excellent fuel economy (3l/100km or ~78 MPG US) it failed in the marketplace because it was too spartan in most other respects. The Audi Duo in the 1990s and the Audi A2 aluminium-frame subcompact also failed to attract sufficient customers.

Small wonder, then, that in these times of structural overcapacity and difficult labor relations, even Europe's largest carmaker feels it cannot afford to satisfy those who want to see bold moves on drivetrain techology for the sake of fuel economy (as opposed to chipping away at the problem). Bold moves, after all, did not get Ford out of its troubles.

Thanks for the info, Rafael. Diesel is more efficient, but is also more complicated and is also more expensive than gasoline car, so the law of diminishing return would apply when making diesel-hybrid, but not the cost. So it seems that commitment toward diesel in Europe has diminished the incentive toward electric hybrid.
But, given the rapidly advancing battery technology with expected significant drop in price of hybrid-size battery pack, it seems that a mild hybrid like Honda's IMA scheme with small battery pack (0.3-0.5 kwh capacity) can be implemented for nearly all gasoline cars without significant cost increase, especially when the alternator, flywheel, starter, bearings and drive belt all combined into one large-diameter but thin IMA disk. BMW's variable-valve-lift design (Valvetronic) can allow for complete shut down of the valves during deceleration, hence will decrease engine drag due to pumping loss and will increase the effectiveness of regenerative braking, just like in the new Honda Civic Hybrid.

Just my two cents on the real world MPG of hybrids - I had a 2004 Honda Civic Hybrid for two years and it came very close to the EPA rated MPG or 48/47, delivering roughly 45 mpg city in warm or mild weather, 40 mpg city in winter (snow, below freezing temps), 40 mpg highway at 70+ mph and 45+ mpg highway at 60mph. I was quite pleased with its mileage performance, and the hybrid price premium wasn't too big (I bought it before dealers started marking them up - my local dealer actually had 6 for sale at the time I bought it!). IMHO, Honda's mild IMA system works as well in the real world as the Prius, though it is simpler and not as "sexy."

why not run the lines for the thermoelectric generator along the length of the exhuast in counterflow fashion (human blood vessels) perhaps the exhaust could then be cooled enough to minimize the muffler as allen Z suggested. Would this then compromise the catalysts?

It would have to be done post-catalyst, ed. Also the materials are still a bit on the expensive side and you need to transfer the heat away at some point in time so there has to be a method to cool the TEGs as well.

I guess I just don't get it, and maybe the rest of you can help me.

This alternator technology involves a charge sensor and a chip - perhaps $1.00 in technology at scale - that reduces consumption 4%. Maybe you also need the glas-mat battery, so now the cost is $5.00.

You add the electric water pump, you get 2% more savings, for probably a cost neutral move.

Now add start-stop, with some cost for regenerative braking, bigger battery, and the alternator/boost engine, and you get another 10%.

So why isn't this standard equipment for all cars? What am I missing?

The thing with the BMW technology is you are sacrificing performance by sticking a small engine in an already great car. What you are doing is reducing the load on the crank shaft from all of these things like the water pump and alternator. The purpose of this technology is for implementing something that has gains in both realms. They are both increasing fuel economy and increasing the engines motive output. And another thing to all of you who would sleep with your hybrid if you could, this is basicly a bolt on product. There is very little in the way of restructuring of major vehicle components as with adding batteries and true regenerative braking. And they are saving all the weight that gets added for those batteries and the like. This means... what the europeans do better than us... the cost of the vehicle will not skyrocket just because of the new technology. This model vehicle will be competative in pricepoint with the same cars it is now. Therefore they will increase sales because the consumer gets increased performance in terms of horsepower and fuel economy.

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