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Power Split Device Explained

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I know this may sound strange coming from a couple [H] muscle car / off-roading enthusiasts, but this explanation of a PSD (power split device), used in the hybrid Toyota Prius, is pretty damn fascinating. There is an interactive chart you can use to see how the power split device works too. You can thank Kyle for the link on this one!

The Toyota Prius is packed with some pretty high-tech stuff, but at the heart of the Hybrid Synergy Drive (HSD) is a simple little device called the Power Split Device, or PSD. The PSD is a planetary gear set that removes the need for a traditional stepped gearbox and transmission components, and also the familiar rev-lurch-rev-lurch of acceleration in an ordinary gas powered car. It acts as a continuously variable transmission (CVT) but with a fixed gear ratio.
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Wow! Such a simple concept yet effective and efficient.
 
Planetary transmissions are very cool. But before anyone thinks is a high tech device, planetary transmissions powered the original mass production automobile, the Model T.
 
Been then done that with the Model T, nice to see toyota is finally catching up ... ha ha
 
trk2 said:
Planetary transmissions are very cool. But before anyone thinks is a high tech device, planetary transmissions powered the original mass production automobile, the Model T.
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iTYPE said:
Been then done that with the Model T, nice to see toyota is finally catching up ... ha ha
Click to expand...

Re-read the article.
It's the way their using the planetary gear set that's new.
The engine is constantly engaged to the planet carrier; motor 1 to the sun gear, and motor 2 the ring gear.
By varying the power/resistance of all three it adjusts how much power is applied through the ring gear to the wheels.

It's a planetary CVT.
 
Yeah, the PSD is really the cool part of the Prius (and other HSD-like vehicles).

The Prius has a transmission that is continuously variable and has so many modes of operation:
- Reverse
- Cruising, power going from engine to batteries
- Fast acceleration, power coming from batteries
- Deceleration, power going to batteries from regen braking
- Engine braking
- Neutral

All of this is implemented without a clutch and without switching gears. The PSD is very simple and very durable.

People can think what they want about the Prius, but find me a car that:
- Seats 4 normal adults comfortably
- Costs under $22,000
- Has cool features like an LCD screen, Bluetooth, a backup camera, and "Smart Key" (doors open automatically based on proximitiy)
- Runs on regular unleaded gas
- Has decent (not fast, but acceptable) acceleration

Drive 15,000 miles per year (mixed city/highway):
- Prius uses 325 gallons (46 mpg), $1090 at $3.35/gal
- Camry uses 625 gallons (24 mpg), $2090 at $3.35/gal

That's about $1000 per year. Over 5 years, you save $5000 in gas by driving the Prius. That makes the $21,000 Prius cost around $16,000 when compared to the Camry. And the Camry starts at $19,000.
 
High tech?

My 1/8th scale gas powered 4WD buggy has 2 planetary differentials in it.
 
Hooligan said:
High tech?

My 1/8th scale gas powered 4WD buggy has 2 planetary differentials in it.
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There's a slight difference between a differential used to allow a vehicle to turn and one used with two precisely controlled synchronous high-voltage AC motors to create a continuously variable transmission.

Mechanically speaking, the Prius transmission is quite simple. That's the genius part.
 
bsoft said:
Mechanically speaking, the Prius transmission is quite simple. That's the genius part.
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In that respect yes. However, if Toyota can ever figure out how to make last 200,000 miles...that will be the genius. This type of system has difficult "wearing" issues to tackle as well as. However, since Toyota has no problem keep tens of thousands of people employed in R&D, they should solve it with enough time.
 
Ford has licensed this technoligy from Toyota and is using it in the trans of their Escape Hybrid.
 
DF454 said:
Ford has licensed this technoligy from Toyota and is using it in the trans of their Escape Hybrid.
Click to expand...

While this is true, your sentence implies that Ford bought the technology from Toyota. Ford independently developed their own hybrid powertrain and then found that Toyota had patented the same process. Ford and Toyota swapped patent licenses to allow Ford to use their hybrid version while Toyota got license agreements from Ford in diesel engine technology. In neither case did Ford or Toyota share designs with each other.
 
thanks for clearing that up about ford. i know they have had CVT for a few years no...i rented a 500 with CVT that was pretty nice.
 
thanks for clearing that up about ford. i know they have had CVT for a few years no...i rented a 500 with CVT that was pretty nice.
 
Trepidati0n said:
In that respect yes. However, if Toyota can ever figure out how to make last 200,000 miles...that will be the genius. This type of system has difficult "wearing" issues to tackle as well as. However, since Toyota has no problem keep tens of thousands of people employed in R&D, they should solve it with enough time.
Click to expand...
The Prius will last 200,000+ miles...
http://www.grist.org/news/maindish/2005/08/02/sainsbury-cab/

If you have reports of the transmissions wearing out quickly, etc... I would like to see them.
The planetary CVT is similiar to a differential in how it works. I don't hear of too many differentials being replaced in vehicles.

The most likely part on the Prius to wear out in 200K miles is the battery pack. That replacement cost will continue to lower as the popularity of the car increases. Comparatively, there is reduced maintenance costs on the other parts of the vehicle, such as the brake pads and the engine. Both of these systems are helped by the electric motors which require very little maintenance as well. So there is a decent trade-off.
 
Trepidati0n said:
In that respect yes. However, if Toyota can ever figure out how to make last 200,000 miles...that will be the genius. This type of system has difficult "wearing" issues to tackle as well as. However, since Toyota has no problem keep tens of thousands of people employed in R&D, they should solve it with enough time.
Click to expand...

What is there too have problems?
The motors and engine are always engaged with their respective planetary piece.
The only points of wear I see are the gear teeth, engine parts and motor bushings.
 
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