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Mazda?s Capacitor Based Automotive Regenerative Braking System

It is called 'i-ELOOP'.Wayne Gerdes - CleanMPG - Nov. 24, 2011
Mazda's 'i-ELOOP' regenerative braking system
Mazda released details on a groundbreaking regenerative braking system that uses a super capacitor in leiu of a battery for quick storage. The system, which Mazda calls 'i-ELOOP', will begin to appear in Mazda's vehicles in 2012. Mazda claims that in real-world driving conditions with frequent acceleration and braking, 'i-ELOOP' improves fuel economy by approximately 10 percent. We know better but there will always be an advantage with regenerative braking rather than throwing it away any time you have to step on the brake.
Mazda's regenerative braking system is unique because it uses a capacitor that temporarily stores large volumes of electricity. Compared to batteries, capacitors can be charged and discharged rapidly and are resistant to deterioration through prolonged use. 'i-ELOOP' efficiently converts the vehicle's kinetic energy into electricity as it decelerates, and uses the electricity to power the climate control, audio system and numerous other electrical components.
Regenerative braking systems are growing in popularity as a fuel saving technology. They use an electric motor or alternator to generate electricity as the vehicle decelerates, thereby recovering a portion of the vehicle's kinetic energy. Regenerative braking systems in hybrid vehicles generally use a large electric motor and dedicated battery.
Mazda developed its regenerative braking system to handle a large influx of current and slowly give it back. And they somehow did it without the use of a dedicated electric motor but instead of a reversing alternator which sounds to me like a dedicated motor generator by a different name?
'i-ELOOP' features a new 12-25V variable voltage alternator, a low-resistance electric double layer capacitor and a DC/DC converter. 'i-ELOOP' starts to recover kinetic energy the moment the driver lifts off the accelerator pedal and the vehicle begins to decelerate. The variable voltage alternator generates electricity at up to 25V for maximum efficiency before sending it to the Electric Double Layer Capacitor (EDLC) for storage. The capacitor, which has been specially developed for use in a vehicle, can be fully charged in seconds. The DC/DC converter steps down the electricity from 25V to 12V before it is distributed directly to the vehicle's electrical components. The system also charges the vehicle battery as necessary. 'i-ELOOP' operates whenever the vehicle decelerates, reducing the need for the engine to burn extra fuel to generate electricity. As a result, in "stop-and-go" driving conditions, fuel economy improves by approximately 10 percent.
There is no way to improve fuel economy by 10% through a 12-25V system but on the Japan Test cycles known to the world as magic pixie dust, maybe 10% is about right?
The name 'i-ELOOP' is an adaptation of "Intelligent Energy Loop" and represents Mazda's intention to efficiently cycle energy in an intelligent way.
'i-ELOOP' also works in conjunction with Mazda's unique 'i-stop' idling stop technology to extend the period that the engine can be shut off.
Mazda is working to maximize the efficiency of internal combustion engine vehicles with its groundbreaking SKYACTIV TECHNOLOGY. By combining this with i-stop, i-ELOOP and other electric devices that enhance fuel economy by eliminating unnecessary fuel consumption, Mazda is striving to deliver vehicles with excellent environmental performance.
SuperCap systems used for hybridization in R&D projects from the past found the Super Cap to be prohibitively expensive with the resultant payback smaller than what was hoped. Who knows, maybe Mazda has discovered the holy grail but when I hear of 12-25V systems returning a 10% increase in fuel efficiency, I will be just as skeptical as I am with SKYACTIV which so far has produced 7 more HP and the same highway fuel economy from the much hyped 2.0L in the new Mazda3 as the standard every day 2011/2012 Elantra with its MPFI 1.8L.
We will have to wait and see?

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Re: Mazda?s Capacitor Based Automotive Regenerative Braking System

Your skepticism is justified. I doubt even powering the alternator with magic would improve fuel economy by 10% in normal circumstances in a non-hybrid car. It would be possible if we assume unusually heavy electrical demands, and a lot of time idling or moving very slowly.

Last edited by RedylC94 : Yesterday at 02:58 AM.

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Re: Mazda?s Capacitor Based Automotive Regenerative Braking System

Regen is meaningful in that it recovers kinetic energy that would otherwise be turned
into waste heat. But it is a lossy system, due the energy conversions between wheel
and battery.
kinetic -> (wheels) -> mechanical -> (gen/alt) -> electrical -> (batt) -> chemical
I've read that in the Prius the energy recovery efficiency is ~40%. A smart Prius driver
minimizes the losses by using regen as little as possible by "driving without brakes',"
traffic and topography permitting. If you're really trying to drive efficiently, regen is a
measure of your mistakes in being caught going too fast in changing real world
conditions.
So, different drivers will see different amounts of regen and determing "real savings"
would require removing the human factor somehow.
Stopped in my Prius w/ScanGuage, I do notice a slow reduction in charge in the HV
battery as it feeds the 12V bus via the DC-to-DC converter. So, Madza's regen system
coupled with the i-Stop would provide an alternate energy source for the "housekeeping"
electrical loads when stopped. I wonder though if the small gains are worth the necessary
extra cost and complexity.
I expect to see the old "What's the payback period?" question come up soon.
All that said, Mazda is to be complemented in doing something to recover otherwise lost
energy. I'd guess that driving in the "Zoom-zoom" style would generate a lot of regen,
but very little energy recovered relative to the amount of fuel that propelled the zooming
in the first place.
.

Last edited by Rokeby : Yesterday at 09:15 AM.

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Re: Mazda?s Capacitor Based Automotive Regenerative Braking System

Quote:

The Prius system allows Toyota to gear it really tall-since the electric motor can kick in to prevent lugging.

Great point. The Prius normally uses the electric motor to get going from a dead stop (assuming the ICE is warmed up). I hadn't thought about the savings from higher gearing, but starting on electric also avoids gas-wasting high throttle/low rpm usage of the ICE.
I'm not a big fan of regen. As rokeby says, braking of any kind, regen or not, is often a sign of inefficient driving: you've wasted energy to get more momentum than you need.
Another problem with regen is that most often it's a high current/short time event. For example, braking to a stop sign or red light: 10-20 seconds of regen?? Batteries recapture charge better from longer, lower current events. The SOC in either of my cars rarely budges after a typical stop like this. Maybe a capacitor captures energy from these events better than a battery does.
What DOES show on the SOC is regen during long descents and gradual decels on long freeway offramps, but these opportunities are less frequent.
I sometimes think that the main advantage of regen is that it reduces wear on the friction brakes so less money spent on brake jobs!!
Mazda's iStop autostop technology seems really great. Apparently they haven't used it more because of the demands on the battery during autostop, and this cap storage is a missing piece of the puzzle.

Last edited by lightfoot : Yesterday at 01:19 PM.

Quote:

I'm not a big fan of regen. As rokeby says, braking of any kind, regen or not, is often a sign of inefficient driving: you've wasted energy to get more momentum than you need.
Another problem with regen is that most often it's a high current/short time event. For example, braking to a stop sign or red light: 10-20 seconds of regen?? Batteries recapture charge better from longer, lower current events. The SOC in either of my cars rarely budges after a typical stop like this. Maybe a capacitor captures energy from these events better than a battery does.

Ok, guys. Step down from your hypermile horse for a moment: brakes are there for a reason. You will need to use them, and likely more in the future as traffic density increases. There's not a way for our road system support 380 million hypermilers unless we leave the driving to computers, otherwise you'll have to always maintain 10x extra spacing for the one person out there that doesn't...
As for the technology, one of the more inefficient pieces of regen braking is the charge loss to the battery. Charging to a capacitor is far more efficient, although not as efficient as directly spinning a mechanical flywheel. In any event, Mazda will be able to get more that the 40% recovery number of the Prius's.
Where Mazda's mild hybrid will still lose out is the lack of a good EV only mode, but this will be as effective as Honda's IMA. At the end of the day, that's all it's about, is using less energy to support the inefficiencies of having a human driver that doesn't want to be efficient.

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Re: Mazda?s Capacitor Based Automotive Regenerative Braking System

I think lightfoot has the key in mentioning i-stop. i-stop works with piston positioning instead of using an auxiliary battery. So, in addition to the gains by use of a smart alternator, and, I presume, higher efficiency in the charge and discharge process, many of the gains with i-eloop may simply be making up for deficiencies in i-stop.
The cost of the capacitors is obviously a key issue. However, just as the Prius' HSD saves by displacing multiple conventional parts, i-stop plus i-eloop displaces the auxiliary start/stop battery, and should reduce the draw from the main 12V battery and extends its life. Then, an extremely durable capacitor would have value at end of vehicle life. However, if large capacitor is heavy if could negatively affecting fuel economy. To become a dominant system the capacitor has to be durable and cheap enough to beat the displaced battery-based systems. But for Mazda's purpose, it just has to be cheap and durable enough to be able to make a profit on it: it does have a coolness factor on its side. I hope it at least indicates some price drops in large capacitors.

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Re: Mazda?s Capacitor Based Automotive Regenerative Braking System

Quote:

Ok, guys. Step down from your hypermile horse for a moment: brakes are there for a reason. You will need to use them, and likely more in the future as traffic density increases. There's not a way for our road system support 380 million hypermilers unless we leave the driving to computers, otherwise you'll have to always maintain 10x extra spacing for the one person out there that doesn't...

Umm, this IS the hypermiling site, so why shouldn't we be on that horse??
Other thoughts:
- I think all hypermilers DO use brakes, we just try to drive so that we are not forced to use them, which also happens to be a big part of safe defensive driving.
- Population of the USA is about 310 million, not all are drivers. About 190 million licensed drivers in 2000.
- I'm baffled why hypermiling would put a strain on the road system. Surely lower speeds would allow increased traffic density??
- Between 30,000 and 40,000 people die in traffic accidents on US highways every year, even larger numbers of serious injuries, so what we're doing now isn't working very well. Maybe it's time to change things??

Quote:

At the end of the day, that's all it's about, is using less energy to support the inefficiencies of having a human driver that doesn't want to be efficient.

Using technology to support unsafe driving by people that don't want to change to safer driving behaviors hasn't worked, so why believe that technology will work any better to make them more efficient? The number of people that manage to get a Prius down to 40mpg is a good hint. Humans are remarkably good at circumventing technology.
It would make more sense to put effort into improved driver training and testing*, retesting for relicensing, traffic enforcement, etc. Changing driving behavior can improve both safety and fuel efficiency at the same time. And lower speeds could enable engineers to design cars so that they are just as crash-worthy at the lower speeds as current cars are at high speeds, only much lighter/smaller, which would improve fuel economy.
So I'm stayin' on that horse, thanks!
* - Given the current political climate, it's unlikely that government would do this, but maybe insurance companies would. In the motorcycle arena, insurance companies more or less force you to take motorcycle safety training before they will insure you, and those courses are supported by the manufacturers and are very good.
I'll leave it there, this is way way OT, apologies!!

Last edited by lightfoot : Yesterday at 01:56 PM.

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