Incorrect or over simplified transmission description.

[okiebutnotfrommuskogee]

Hi Group,

This is my first attempt at starting one of these from scratch. I hope it comes out right.

From time to time to time I get emails from our Toyota dealer. The most recent one had a link to an article about the 2008 Prius. In it was a very brief description of the transmission. Here is a quote from it.

" Prius uses other technologies to gain fuel efficiency, too. For instance, its transmission, a continuously variable automatic (CVT), substitutes a belt and pulley system for conventional gears to create a near-infinite number of drive ratios. Thus, the transmission will use the most efficient ratio to transmit power to the drive wheels. "

That sounds more like the CVT that was in the Civic Hybrid that I owned for almost five years before buying the 07 Prius and selling the Honda. By the way, that transmission had to be replaced twice in 45,000 miles.

Here is a link to the complete article. http://www.imakenews.com/jimnortontoy/e_ar...bnrV0K,b5gk0QrS

Are they right or are they wrong?

[Danny Hamilton]

<div class='quotetop'>QUOTE(okiebutnotfrommuskogee @ Oct 10 2007, 09:40 AM) [snapback]523574[/snapback]</div>

Are they right or are they wrong?
[/b]

They are wrong.

[9G-man]

<div class='quotetop'>QUOTE(okiebutnotfrommuskogee @ Oct 10 2007, 10:40 AM) [snapback]523574[/snapback]</div>

Hi Group,

This is my first attempt at starting one of these from scratch. I hope it comes out right.

From time to time to time I get emails from our Toyota dealer. The most recent one had a link to an article about the 2008 Prius. In it was a very brief description of the transmission. Here is a quote from it.

" Prius uses other technologies to gain fuel efficiency, too. For instance, its transmission, a continuously variable automatic (CVT), substitutes a belt and pulley system for conventional gears to create a near-infinite number of drive ratios. Thus, the transmission will use the most efficient ratio to transmit power to the drive wheels. "

That sounds more like the CVT that was in the Civic Hybrid that I owned for almost five years before buying the 07 Prius and selling the Honda. By the way, that transmission had to be replaced twice in 45,000 miles.

Are they right or are they wrong?
[/b]

That description is partially correct, but misleading. The heart of the Prius CVT, continuously variable part, is the planetary gear that links the drive components. It's unlike anything on the road. That is linked to the final drive by a (metal)belt drive . Hence the misleading and misunderstood belt part.

[ACORNBLUES]

wrong wrong and dead wrong. the prius uses an eCVT. e because it makes use of electric motors to change the ratio of the final output.

[9G-man]

<div class='quotetop'>QUOTE(ACORNBLUES @ Oct 10 2007, 02:58 PM) [snapback]523728[/snapback]</div>

wrong wrong and dead wrong. the prius uses an eCVT. e because it makes use of electric motors to change the ratio of the final output.
[/b]

What's in the red circle? A Belt. Any questions? And those electric motors you speak of are connected to the planetary gear, which is connected to the final drive by that belt.



[attachmentid=11942]

[jhinton]

<div class='quotetop'>QUOTE(9G-man @ Oct 10 2007, 10:17 PM) [snapback]523995[/snapback]</div>

What's in the red circle? A Belt. Any questions? And those electric motors you speak of are connected to the planetary gear, which is connected to the final drive by that belt.
[attachmentid=11942]
[/b]

The circled item is not a belt (rubber) it is a chain (metal)

[9G-man]

<div class='quotetop'>QUOTE(jhinton @ Oct 10 2007, 11:33 PM) [snapback]523999[/snapback]</div>

The circled item is not a belt (rubber) it is a chain (metal)
[/b]

<div class='quotetop'>QUOTE(9G-man @ Oct 10 2007, 11:21 AM) [snapback]523596[/snapback]</div>

That description is partially correct, but misleading. The heart of the Prius CVT, continuously variable part, is the planetary gear that links the drive components. It's unlike anything on the road. That is linked to the final drive by a (metal)belt drive . Hence the misleading and misunderstood belt part.
[/b]

I already said metal. I think you are now pushing symantics. Belt, chain. Is that really the issue? I agree it's best referred to as a chain.

[patsparks]

That metal chain(belt if you like) has a fixed number of links with a fixed number of teeth inside it, the 2 gears it engages also have a fixed number of teeth and none of the components change size in any way to alter the ratio. The CVT part of the transmission is all in the way the 2 motor/generators and the battery interact with each other controlled by the HSD computer. A reduction ratio is created in effect by allowing some of the ICE's power to go into the smaller generator via the power split device (a planitary gear set with fixed ratios also) allowing the engine revs to increase then feeding that power to the larger of the 2 motors to make additional torque to drive the vehicle. When even more power is needed for short times additional power is drawn from the battery to power the larger of the 2 motors making even more torque to propel the vehicle.

Neither the battery or the smaller generator have the capacity on their own to drive the larger motor at full power but working together the battery and the small generator (taking power from the ICE) drive the larger motor at full power. At the same time the computer controls the load on the engine via the smaller generator, valve timing and throttle to keep the ICE running at its most efficient speed and load.

I hope I used small enough words.

The real issue is that there is no variable belt drive in the 04 - 08 Prius.

[9G-man]

[quote=patsparks @ Oct 11 2007, 12:02 AM) [snapback]524008[/snapback]</div>

That metal chain(belt if you like) has a fixed number of links with a fixed number of teeth inside it, the 2 gears it engages also have a fixed number of teeth and none of the components change size in any way to alter the ratio. The CVT part of the transmission is all in the way the 2 motor/generators and the battery interact with each other controlled by the HSD computer. A reduction ratio is created in effect by allowing some of the ICE's power to go into the smaller generator via the power split device (a planitary gear set with fixed ratios also) allowing the engine revs to increase then feeding that power to the larger of the 2 motors to make additional torque to drive the vehicle. When even more power is needed for short times additional power is drawn from the battery to power the larger of the 2 motors making even more torque to propel the vehicle.

Neither the battery or the smaller generator have the capacity on their own to drive the larger motor at full power but working together the battery and the small generator (taking power from the ICE) drive the larger motor at full power. At the same time the computer controls the load on the engine via the smaller generator, valve timing and throttle to keep the ICE running at its most efficient speed and load.

I hope I used small enough words.

The real issue is that there is no variable belt drive in the 04 - 08 Prius.
[/b]

Excellent description of how the ratio is varied.

QUOTE(9G-man] Oct 10 2007, 11:21 AM)
That description is misleading. The heart of the Prius CVT, continuously variable part, is the planetary gear that links the drive components. It's unlike anything on the road. That is linked to the final drive by a (metal)belt drive . Hence the misleading and misunderstood belt part.[/b]

I never inferred that the chain (regreting I typed belt, ) drive varied the output ratio. Just that it linked the primary drive (planetary gear PSD) with the final drive. It's simply the presence of the chain that has caused the confusion with a conventional belt CVT.

[Tech_Guy]

For a really good detailed technical description of the Prius "transmission", goto the following URL:

http://www.cleangreencar.co.nz/page/prius-transmission


Keith