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Old 07-03-2012, 08:05 PM   #11 (permalink)
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Aren't planetary gears simply... one gear?

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Old 07-03-2012, 09:04 PM   #12 (permalink)
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But I really thought it was the fact that CVTs got a 6% boost and a dual clutch got a 7% boost that stood out most! Is that unicorn poop or due to the frictional losses common to CVTs.
The electric CVTs of Toyota and Ford suffer when one of the motors needs to provide torque near 0 RPM. The electric motor efficiency there is low. Belt type CVTs have some slippage.

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It would be better to compare two similar cars with different (hybrid and non-hybrid) drivetrains.
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Sure, but you'd also have to make sure they have equal performance, especially acceleration.
I think the Lincoln MKZ is a fair example, but the V6 is substantially quicker than the hybrid, 0 to 60 in 7.2 for the V6; 8.7 for the hybrid. The EPA combined is 21 MPG for the V6 and 39 mpg for the hybrid. (The list price is the same.)

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Old 07-03-2012, 09:22 PM   #13 (permalink)
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Quote:
Originally Posted by niky View Post
Aren't planetary gears simply... one gear?
a planetary gear has a few gears:
1 sun gear-which is typically the drive gear
2 (or more) planet gears-which connect the sun to the planetary gear
1 planetary gear- which is a large ring that touches the planet gears.

So there is a tiny gear, surrounded by more similar sized gears, wrapped in a larger circle.
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Old 07-03-2012, 10:37 PM   #14 (permalink)
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...it's all about simple mathematics:

90% = 90% (one conversion)

81% = 90% of 90% (two conversions)

73% = 90% of 90% of 90% (three conversions)

66% = 90% of 90% of 90% of 90% (four conversion)

...the fewer times you convert energy, the "...more of it (energy) you have...", or stated conversely the "...less you've lost."
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Old 07-04-2012, 07:11 PM   #15 (permalink)
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Originally Posted by niky View Post
Aren't planetary gears simply... one gear?
Hello niky,
I saw MPGranger's post, and I didn't think it really addressed your question.
I'm assuming you know what a planetary gearset is, and you've seen or studied them for aircraft or toys or something. So yes, a single planetary gearset presents one gear ratio.

But for something like an automatic transmission, in general using planetary gears you need one planetary system for 2 ratios, plus you need an additonal planetary set as a reverser. So for a 6 speed transmission you need 4 gearsets.
Matthieu Rihn developed the "ravigneaux" gearset using 2 sun gears, 2 ring gears and 1 planet carrier. By using clutches and brake bands, you can have 2 planetary gearsets produce 3 forward ratios and reverse.

However, the planetary CVTs that vskid3 was referring to is the electrically controlled "power-split device" used in the Prius and other hybrids. It is based on the 1970s U.S patents 3,566,717 and 3,732,751.

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Old 07-05-2012, 12:19 AM   #16 (permalink)
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Thanks... I'll check it out... having seen some diagrams and driven the Prius... I still can't wrap my head around the thing!
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Old 07-06-2012, 08:26 AM   #17 (permalink)
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HowStuffWorks "How Automatic Transmissions Work"

HowStuffWorks "Toyota Prius: Lots More Information"
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Old 07-06-2012, 02:41 PM   #18 (permalink)
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The current Hybrid technology appears to be in jeopardy of being overtaken by advances in ICE. However there is a new evolution of Hybrid technologies that could prove to be much better once critical mass of production and acceptance reduces manufacturing costs. Anything that gets away from using batteries is a plus!
Here's an article on the flywheel Hybrid advances that is worth a read.

KERS of the hybrid car:Flywheels and ultracapacitors give you a 10-second jolt | ExtremeTech
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Old 07-06-2012, 02:57 PM   #19 (permalink)
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Quote:
Originally Posted by niky View Post
Aren't planetary gears simply... one gear?
One gear, by itself, is pretty useless as a means of power transmission. To change ratios- the purpose of having gears in the first place- requires at least a second gear so that there's a gear mesh. Then there's the planetary gears, usually illustrated with 5 gears and 6 meshes.
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Old 07-06-2012, 03:24 PM   #20 (permalink)
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There is no amount of improvement in an ICE that can get it to be even HALF as efficient as an electric motor. The best electric motors are about 94% efficient, and I very much doubt that any ICE (or ECE for that matter) will ever exceed 47% efficiency peak; let alone average above 42%.

So I think that all efficient cars in the future will have battery packs and plugs. The only question in my mind is whether they also have an engine, and how they use that engine i.e. in a serial or in a parallel mode.

Before you get all excited, you have to think about how an engine works best: and that is at a narrow range of RPM; and in "bursts". All those MPG contests when the cars get >1,000MPG only have a very small engine and they only run the engine in short bursts and at a very specific RPM. These cars are hardly practical in the real world.

Contrast this with the SolarWorld GT car built by Bochum University, which is relatively practical and very efficient -- it only uses solar PV panels on the car, and it is driving around the world.

Another example is the Edison2 VLC: the ICE version got 110MPGe on the EPA Combined test -- which is fabulous for a 4 seat car. But the electric version got ~245MPGe, and an AC electric drivetrain probably would be over 300MPGe, and it would be far quieter and a lot quicker, and smoother, etc.

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