How does Nissan's battery-free e-4WD work?
To assist their gas engines, Nissan has developed e-4WD, or electric four wheel, which uses electric motors but has no batteries. Is this a hybrid? Yeah. Think of it as a mild series or serial hybrid, which is a kind of hybrid that uses a generator instead of a battery to power the electric motors. Wait a minute, you might say: aren't four wheel drives less efficient than two wheel drive cars? Yes but e-4WD is very light and compact because it's electric.
Okay, so how long before the fuel savings pay for the added hardware? It's not that clear because e-4WD is only used on a few specialized vehicles like Nissan's March (see video below the fold). Estimating exactly how much a hybrid improves fuel efficiency is not a trivial task but as more vehicles use e-4WD, it should become clearer. Also, the system's primary goal is not improving efficiency but horsepower (Torque: 109 pound-feet, Horsepower: 90 hp). Performance ... hybrids? "That's an oxymoron" you might say, laughing, before you remember what Lexus is up to.While the idea is rejected by most automakers Nissan is planning to make performance hybrids. Greens like the growl of a good engine and watching a guy get smoked in a race, even if the EPA thinks it's a contradiction. Soon, when talking about a hybrid, you won't just ask how much more fuel efficient is it but how much more POWER does it offer. The lack of a battery in the e-4WD should keep the costs low as well.
Related:
[Source: Nissan]
Reader Comments (Page 1 of 1)
Tony Belding 1:42PM (2/02/2008)
According to Bob Lutz, you shouldn't call this vehicle a "hybrid" at all. Since only the electric motors actually propel the vehicle (as with the Chevy Volt), it must be referred to as an EV or REEV.
It's a 100% pure electric vehicle. . . that you have to fill at the gas pump. The ultimate in greenwashing.
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Lascelles Linton 2:16PM (2/02/2008)
Tony Belding, I should have been clearer but there is a gas engine that drives the car most of the time.
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Lascelles Linton 3:29PM (2/02/2008)
I added "to assist their gas engines."
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Tony Belding 4:30PM (2/02/2008)
Wait, wait. . . If I'm looking at the diagram right, it actually uses the ICE to drive the front wheels and the electric motor to power the rear wheels?
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GoodCheer 4:56PM (2/02/2008)
At first I was baffled by this drive architecture. It's a bit confusing that there is no electricity storage. What's the point?
The point is that you get power to the two other wheels with less weight (??) and fewer geometrical restrictions than would be required to run a shaft down the middle of the car. Thus the name, e4WD... it's simply a 4WD system.
All the same I'm stunned that with all the great options for energy storage (supercaps, ever-better batteries) they would not include even a little bit of energy storage to imporve mileage and/or performance.
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Travis Rassat 4:59PM (2/02/2008)
I like this concept because it could allow for more open vehicle platforms. You're essentially trading traditional driveshaft power transfer for electric wire power transfer. Rather than designing the car's passenger and cargo areas around the drivetrain, you can design the drivetrain around the desired passenger and cargo areas. I think it's a cool twist and could really allow designers to come up with some cool vehicles that make more efficient use of their platform.
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Lascelles Linton 6:52PM (2/02/2008)
Tony Belding, Yeah... NO BATTERY :D Kinda strange! GoodCheer, I am guessing the saving come from reducing the size of everything. An equivalent 2WD would probably be more efficient ... BUT a 4WD would probably be less efficient AND less powerful without e-4WD.
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carnut 4:22AM (2/03/2008)
With so much expertise on the comment section, anyone wonder where the extra 'power' is coming from, to deliver 'performance', when the only power producer on-board is the engine?
Let me answer, because this is a clever sleight of hand from nissan (most likely a Hitachi-made system).
What you're seeing is just a way to create a different ratio 'transmission' at the rear wheels without the propshaft going fore-aft of the vehicle, and all that you are getting here is TORQUE, not power, at the rear wheels, and when you add up all powers (power from engine = power to front wheels + power to rear wheels, as against power from engine+battery = power to front and/or rear wheels), you realize that this makes the engine produce / split power fore-aft as desired by adjusting front and rear gear ratios (the rear gear ratios are simply a mathematical conversion of torque delivered to power at generator to torque out of the engine).
Bottom line- engine produces all power to go to the front and rear wheels, only its distribution to the rear wheels is electric rather than mechanical.
So, don't expect this car to do any 'electric-only' driving or regenerative braking and if the engine is off, you can bet the car is turned off as well. There even won't be an idle-engine-off mode.
So, this is not really a hybrid at all. It has gasoline engine and an electric torque split device. The car may even launch with rear electric motor alone (nice performance), but you can bet the engine will be on at all times.
I know lots of you are scratching your heads now, and that's fine.
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GoodCheer 11:08AM (2/03/2008)
I think carnut might be onto some thing when he says
"The car may even launch with rear electric motor alone (...)".
This system could operate as a series hybrid for low speed or variable speed operation (albeit without any regen), and operate as a direct drive ICE for constant speed operation. In that sense, it is a pure parallel hybrid (though turned on it's head, in a way).
By the way, I am scratching my head at the statement "(...) all that you are getting here is TORQUE, not power, at the rear wheels, and when you add up all powers (power from engine = power to front wheels + power to rear wheels (...)"
The only time you get torque without power is when the wheel is not turning. power = torque * rotational velocity.
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Carnut 8:46PM (2/03/2008)
@GoodCheer-
You're right - eAWD does deliver power to the rear wheels at non-zero speeds, and consumes lots of energy even at zero speed, *if* it is providing stall torque (I-squared-R in the motor) to hold the vehicle against, say, grade.
HAving the electric motor at rear axle gives the advantage of engine only having to provide the desired power (at the minimum possible RPM), while the generator/motor combination can deliver the required amount of torque at the rear wheels - a nice setup for a good launch feel.
The reason I said torque and not power is because the power still comes from engine, not a battery as the case would be for a hybrid. So, all that this setup does is to enable adding an eAWD to any FWD application without the investment into redesigning the floor-pan to accommodate fore-aft propshaft and avoiding the mechanical inefficiencies of a diff / propshaft setup that spins all the time. I saw patents / SAE papers putting the estimates of 5-7% fuel economy improvements for this type of a system. I don't buy this personally, as the mechanical drives have become fairly efficient and real-world improvement will depend on the duty cycle (as in 'your mileage may vary') and the efficiency of the generator/motor system, which is used only 'on-demand'.
So, on the whole, a nice idea that has been around for at least 10+ years, but is seen in production form for the first time.
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