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?
<div class='quotetop'>QUOTE(okiebutnotfrommuskogee @ Oct 10 2007, 09:40 AM) [snapback]523574[/snapback]</div> They are wrong.
<div class='quotetop'>QUOTE(okiebutnotfrommuskogee @ Oct 10 2007, 10:40 AM) [snapback]523574[/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.
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.
<div class='quotetop'>QUOTE(ACORNBLUES @ Oct 10 2007, 02:58 PM) [snapback]523728[/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]
<div class='quotetop'>QUOTE(9G-man @ Oct 10 2007, 10:17 PM) [snapback]523995[/snapback]</div> The circled item is not a belt (rubber) it is a chain (metal)
<div class='quotetop'>QUOTE(jhinton @ Oct 10 2007, 11:33 PM) [snapback]523999[/snapback]</div> <div class='quotetop'>QUOTE(9G-man @ Oct 10 2007, 11:21 AM) [snapback]523596[/snapback]</div> 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.
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.
For a really good detailed technical description of the Prius "transmission", goto the following URL: http://www.cleangreencar.co.nz/page/prius-transmission Keith
Thanks Keith, What I tried to do was keep my description as simple as possible without going into too much detail. I know it isn't covering all the operating parameters of the HSD but I was trying to illustrate how the HSD achieves infinite "ratios" in the transmission. The page you have linked is excelent and I recomend everyone who wants a plain english description of the works of the HSD read it from end to end. It doesn't go into too much fine detail either but quite a bit more than my simple description. Good find!!
<div class='quotetop'>QUOTE(patsparks @ Oct 11 2007, 02:21 AM) [snapback]524072[/snapback]</div> I first posted this thread because I already knew how the Prius transmission works and thought that the way it was presented in the article from Toyota made it sound like a very poor excuse for a transmission. Anyone interested in a Prius might be turned off by what it said. They might as well have been talking about my riding lawn mower. The part circled in red in the above pictures is actually a chain not a belt and transfers the power to the final drive after it comes from the variable part of the transmission. I think that the HSD is a wonderful piece of engineering. I suppose that the only other hybrids with it are the ones that Toyota has granted licenses to. As I said before, I owned a HCH for almost five years before getting the Prius. It's CVT used a metal belt that ran between two variable pulleys. I don't believe that the troubles it had were with the belt, but instead, were with the start-up clutch. Bad chattering when starting up under load. The worse the load or steeper the incline, the worse the chattering. Honda replaced it twice at no cost. I liked the HCH fine until I drove a Prius for a day while my Avalon was in for some warranty work. I had no plans to get rid of the HCH, but that day long experience with the Prius did it. Less than two weeks later there was a new Prius in the drive way and in another week, the HCH had a new owner. Here is a picture of the HCH variable transmission. Note the steel belt and the pulleys. http://www.wbcoxco.com/cvt01.jpg
Does the early Prius have a variable belt? I read once that it did. (Edit, just found out it doesn't) Thanks for starting the thread, I knew where you were coming from but it has lead me to do some interesting research and reading because of where it went.
You can also play with a functional model of the PSD on my site, here. I initially had some of the same confusion about how it works, and having the tools at my fingertips, I had to model it to really learn just how cool the Prius transmission is! No variable belt. No clutch. No starter motor. No transmission in the sense that other cars use it. Think of what you've spent replacing some or all of those components on other cars. Fun stuff!
<div class='quotetop'>QUOTE(ACORNBLUES @ Oct 10 2007, 02:58 PM) [snapback]523728[/snapback]</div> Sorry, but that's wrong, too. Toyota referred to the early Estima hybrid, which had a conventional belt-and-cone CVT transmission and a parallel electric motor, as "eCVT". The current Estima is a series-parallel hybrid. Want more confusion? Ford refers to the Escape series-parallel hybrid as eCVT. These are marketing terms, folks. Stick with engineering terms, and you'll be on track. <div class='quotetop'>QUOTE(okiebutnotfrommuskogee @ Oct 10 2007, 10:40 AM) [snapback]523574[/snapback]</div> Wrong, but ANY transmission that can output a continuously variable drive ratio is a CVT. However, since the only popular type of CVT (prior to Toyota's version) has been belt-and-cone, even technicians get confused. Say "CVT" and they will look for the belt and the cone.
