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Old 04-25-2013, 02:43 PM   #1
warpath
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Default Volvo’s Flywheel Hybrid Reduces Consumption By 25 Percent

Automobile: http://rumors.automobilemag.com/volv...#axzz2RVBnXfEL











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Volvo says that tests on public roads showed its kinetic flywheel hybrid system can reduce a car’s fuel consumption by as much as 25 percent. The system allows a car with a four-cylinder turbocharged engine to perform as well as one with a six-cylinder engine, yet use much less fuel. Based on these results, Volvo will now consider fitting the technology to a production car.
The Flywheel Kinetic Energy Recovery System uses a 13.2-pound, 7.9-inch carbon-fiber flywheel encased in a vacuum. A special transmission links the flywheel to the rear wheels so under braking, it spins up to 60,000 rpm. Then under acceleration, the flywheel connects to the rear wheels to provide up to 80 hp of extra power.
The flywheel’s boost can reduce the Volvo test car’s 0-to-60-mph time by at least one second, but by allowing the regular engine to turn off at a stop or under light acceleration, it can also improve fuel economy by 25 percent. Volvo says the system is so effective that in the European fuel-economy test cycle, the engine could be turned off almost 50 percent of the time.
Volvo experimented with flywheel hybrid technology as far back as the 1960s, but back then the system used steel flywheels that were heavy, expensive, and inefficient. The automaker claims its carbon-fiber unit would be much cheaper than a typical battery hybrid system.
If Volvo decides to put this technology into production, it could be attached to the four-cylinder VEA (Volvo Environmental Architecture) engines that will launch this fall. The Swedish company has publicly committed to selling cars primarily with four-cylinder engines to reduce fuel consumption. In fact, that commitment means Volvo won’t pursue a large luxury car that might use a V-8 or V-12 engine.
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Old 04-25-2013, 02:49 PM   #2
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Can someone explain how this works? The description is not doing it for me.
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Old 04-25-2013, 02:59 PM   #3
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Originally Posted by Integra96 View Post
Can someone explain how this works? The description is not doing it for me.
The text seems to make sense, if you apply a bit of handwaving to the CVT on the diagram:

Quote:
A special transmission links the flywheel to the rear wheels so under braking, it spins up to 60,000 rpm. Then under acceleration, the flywheel connects to the rear wheels to provide up to 80 hp of extra power.
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Old 04-25-2013, 03:01 PM   #4
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I could be wrong... but this seems like a through-the-road system.

Separate from the front drivetrain, which propels the car primarily.

The rear wheels are pulled along with the car, creating input rotation, fed into the rear axle, through the CVT module, that spins up the flywheel. the CVT variable ratio is so that steady wheel rotation can be translated into increasing flywheel speed, until the flywheel reaches it's max operating RPMs, and is kept there.

There is likely a clutch unit in the CVT, or between it and the flywheel, that allows the flywheel to keep spinning under momentum when the car is decelerating or stopped for a short time.

Upon acceleration, the kinetic energy flow is reversed, a clutch engages, and stored kinetic energy in the flywheel is applied to the CVT, which then variably applies that torque input to the rear axle, as a propulsion force, in addition to the front drivetrain. The front drivetrain works less hard during that acceleration, and saves fuel that would otherwise be used.

It may help some during standing start accelleration, or start-and-stop traffic, but would really flatten out the front drivetrain's demand, if the flywheel can impart the torque to the rear wheels to accelerate up hills, and recover energy when coasting down hills, instead of varying the throttle on the front drivetrain engine.
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Old 04-26-2013, 09:39 AM   #5
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I will simplify it.

Every try to stop a bicycle tire when it is spinning?

this is the same thing. A flywheel is an energy storage device. It is as simple as that. Instead of electical energy, it stores kinetic energy (or energy derived from motion).
the car drives along and spins the flywheel up. It stays spinning due to its low friction bearings and the vacuum it is spinning in (nice touch with the vacuum). When the car comes to a stop, the engine shuts down adn the flywheel keeps spinning. It has rotational inertia that can be used the same way a spinning crankshaft spins. The flywheel starts the car instead of the internal combustion engine.. it is really quite neat.

Hip, word of advice from a dear friend.

If you cannot explain something simply, you do not understand it well enough...

--Albert Einstein.
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Old 04-26-2013, 11:36 AM   #6
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That's what I was thinking - it just seems hard to believe that a spinning flywheel would have enough energy to reduce the load of moving a 3,500 lb. car that much.
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Old 04-26-2013, 11:47 AM   #7
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That's what I was thinking - it just seems hard to believe that a spinning flywheel would have enough energy to reduce the load of moving a 3,500 lb. car that much.
It is a trade-off, like amps and volts multiplying to make watts.

You can make watts with few volts, and many amps, or you can make watts with few amps and lots of voltage.

It isn't that the flywheel is heavy that constitutes the stored kinetic energy, it is that it is spinning FAST.

60,000 RPMS with modest mass, is still an appreciable amount of kinetic energy, just as a much larger mass at 6000 RPMS.

And please do keep in mind... this is not the primary drivetrain, nor is it intended to solely propel the car without the primary drivetrain.

It is supplemental energy recovery and re-use. It helps reduce demand on the front engine drivetrain, it doesn't replace it.

A modest car needs sometimes as little as 8 horsepower to maintain speed on the highway.

Even double or triple that, 16-24 horsepower... may well be enough to maintain cruise control set speed up an incline on the highway, without opening the engine's throttle any more than it would be on a flat level section of highway.

If the flywheel can propel the car up a hill, and recover it's RPMS when coasting down the other side, it keeps that demand off of the front engine, and reduces the engine's fuel input.

And if the flywheel's energy is used first, and mostly depleted, the engine can take over with more throttle application, and the flywheel has still reduced some fuel useage, by recycling some of the car's inertial kinetic energy by being a mass in motion.
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Old 04-26-2013, 12:14 PM   #8
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Originally Posted by Integra96 View Post
That's what I was thinking - it just seems hard to believe that a spinning flywheel would have enough energy to reduce the load of moving a 3,500 lb. car that much.
60,000 rpm is serious business. Angular momentum, yo.
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Old 04-26-2013, 12:46 PM   #9
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60,000 rpm in a vacuum... perhaps I missed the weight of the flywheel, but if it were even 20 lbs, that is a lot of energy stored.

OK, I just did the math on this using what I think are real potential parameters for the system:

If the flywheel weighed 10kg (~22lbs) and was 20cm in diameter (7.9 inches) (and the mass is assumed to be distributed equally across the diameter of the flywheel) and it is slowed from 60,000 rpm to 0 rpm over 5 seconds (typical time getting on the freeway), it provides a continuous 40 N-m of torque or 29.5 ft-lbs.

If the wheel is heavier or larger diameter, the output would be even more. Impressive.

Last edited by kpluiten; 04-26-2013 at 01:16 PM.
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Old 04-26-2013, 02:29 PM   #10
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The weight will be biased toward the rim if they built it correctly
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Old 04-26-2013, 02:54 PM   #11
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Yeah I get the physics - I just needed to look at kpluiten's math. Thank you, kind sir.
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Old 04-26-2013, 03:03 PM   #12
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now upon closer inspection, I am starting to think the flywheel turns a hydraulic pump that powers the CVT...

I need to do more research.
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Old 04-26-2013, 03:27 PM   #13
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Flywheel is 13.2#. Williams F1 went this way during the KERS wars before the McLaren system became the formula, I always thought it seemed like a very elegant solution. They were looking into selling the technology for adaptation into road cars, I wonder if that is where Volvo got this?
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Old 04-27-2013, 12:15 PM   #14
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^Funny, Williams F1 KERS system was the first thing I thought of when I started reading the article. Article does say that Volvo did experiment with hybrid flywheels in the past (1960's) so probably their own design.
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Old 04-27-2013, 06:14 PM   #15
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this is very interesting. so it's not electrically powered, correct? therefore, no batteries to recharge, and no electric motors to power? it looks like it's a self-contained, added-on module. i don't know the standard layout of cvt transmisisons, so i don't know how integral the flywheel module is into the transmission.

at the risk of not understanding the answer, why did they attach the flywheel module to the transmission instead of in between the output shaft and the driveshaft? if it could be used in between the output shaft and the driveshaft, then it could be used on all kinds of transmissions, and almost be a universal device. this is all based on the loose understanding of it storing and using inertial energy.
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Old 04-27-2013, 06:46 PM   #16
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I'd imagine the CVT is needed to translate from 60,000 rpm to road speed/(wheel circumference * axle ratio) rpm.
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Old 04-27-2013, 07:12 PM   #17
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Quote:
Originally Posted by shikataganai View Post
I'd imagine the CVT is needed to translate from 60,000 rpm to road speed/(wheel circumference * axle ratio) rpm.
When the flywheel is powering the car, the road speed would be increasing as the flywheel speed is decreasing. The CVT would have to continuously change the gear ratio to match the two, and while I don't know how they do this exactly, naively this seems to involve ridiculous spread of gear ratio. (Or maybe they just disconnect it once the flywheel speed reaches below 10K RPM or something?)

The other concern would be safety. In an accident, you probably don't want a carbon fiber frisbee spinning at 60K RPM to fly off into the windshield of a car passing by. That vacuum enclosure would have to be extremely sturdy.

I do like the thought of the flywheel spinning all night in vacuum while the car sits in the garage. (I assume the friction of the bearing is low enough for this to happen.)
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Old 04-27-2013, 08:01 PM   #18
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All those salivating about this, you all saw Porsche's flywheel-in-the-passenger seat racer from a few years back, no?

http://www.popularmechanics.com/cars...ybrid-flywheel



Looking at that may offer an explanation for how the mechanics, er, electrics work: Sure looks like a rotor and stator. Conversion to/from electricity would be a much easier way to couple the flywheel, as it were.
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Old 04-27-2013, 08:09 PM   #19
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Quote:
Originally Posted by shikataganai View Post
Conversion to/from electricity would be a much easier way to couple the flywheel, as it were.
That's what I was thinking as well. Using the flywheel instead of the battery in a hybrid like setup seems much easier than using the CVT to connect it directly to the wheel. But what do I know.
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Old 04-27-2013, 11:41 PM   #20
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That's what I was thinking - it just seems hard to believe that a spinning flywheel would have enough energy to reduce the load of moving a 3,500 lb. car that much.
You'd be surprised how much energy big spinning objects have. Where I work, one product line we make is centrifuges and rotors. Our new systems can handle a 12liter capacity centrifuge (28" diameter rotor) exploding. Here's an article from when an older machine using a non compatible rotor exploded.

Skip down to "description of accident"
http://www.chem.purdue.edu/chemsafet...ugeDamages.htm

This was a 1/2" thick steel safety door that buckled. The rotor used was probably only about 14" in diameter.



Here's another failure. 20lb billet titanium rotor split in half at 55k rpms. At that speed, the outside edge is going as fast a .22 bullet. Since this failure was with a rotor meant for the system, the system was able to contain it.

http://web.mit.edu/charliew/www/centrifuge.html



These are smaller, lighter items spinning at a lower speed than that system in the KERS.
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Old 05-03-2013, 12:16 PM   #21
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The porsche module is mounted with the axis of the rotor in the vertical, while the volvo diagram suggests they may mount it with the axis parrallel to the axle. I would think they would need to change to the orientation used in the Porsche to avoid giving the car some really ugly handling characteristics. Having it in the vertical might actually be useful from a handling perspective where it would tend to resist body roll and front-rear pitch changes, as well as vertical displacement, thus giving a smoother ride.
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