Differences between V and non V CVT?

The v definitely doesn't have it

All Primes definitely do.

The PiP was the question mark. So if the PiP doesn't have it, then EV mode travel is speed limited, unlike the Prime- meaning you're not losing a feature.

If the PiP did have that clutch, you're potentially giving up a feature or having to do more work to integrate a clutch.

 

i think the pip is limited to 84mph, but i could be misremembering. i've never gone that fast

 

Without the one-way clutch, the engine would be forced to spin starting around 40mph. And if you're going to spin it, you might as well run it.

 

No, I mean the one-way clutch.

There's a priuschat thread for it as well.

While we're rolling, I understand the v transaxle also has a pitch suppressor (probably not the right name) but I had understood that to be an electronic feature- something in the MG2 inverter control. The idea was that it could dampen or eliminate rhythmic pitching sensations related to the longer wheelbase of the v.

And just other stuff to think about: does the v transaxle inverter(s) give you what you need with respect to air conditioning and power steering?

 

I can't really vouch for the picture in an old Prime marketing brochure.

But the important part is that you're able to spin the planet carrier freely and easily without making the engine turn. If you were to try back-spinning the planet carrier, it would immediately dig in and force the engine to rotate.

With one-way clutch: EV mode goes as fast as the battery allows

Without one-way clutch: EV mode cancels/stops being useful from about 40mph on up... engine starts and helps out from there to the top of the speedo.

 

If you take the flywheel right off a Prius Prime engine, you see this on the back of the engine block:



Notice the circle of fixed teeth around the crankshaft bearing. (They look sloppy because of grease on them. They look tidier without the grease.)

That right there is the (PNC 32528) "1-way clutch holding plate". It's just fixed, immovable, bolted down on the back of the engine block.



If you then put the 35790D "1-way clutch assembly" back on and take a picture of the boring side, it looks, well, boring, and you don't see what's going on with the teeth.



The less boring side of it is the other side, but the member who started that thread didn't take a picture of the interesting side, and there don't seem to be a lot of other pictures of it in the wild. Oh, well.

But there are generic videos on how sprag clutches work:

In the Prime, of course, it's the inner portion of that clutch that is fixed: the teeth on the fixed holding plate. The rotating part is the outer part and is able to spin freely in the normal engine-operating direction, but will engage the fixed teeth and never let the engine spin backwards.

When the engine is turning in the normal direction, those little sprag elements in the rotating part are held outward by centrifugal force and they don't even contact those center teeth, so there's no added friction or ratchety noise.

So, the sprag clutch is something you see on the back of the engine block, and on the engine-facing side of the flywheel. It isn't anything you see just taking the transaxle off, or looking at its damper, which goes between it and the flywheel.

The parts diagram above is funny, because it shows both 1-way clutch pieces, and then next it shows the transmission input damper, and it doesn't show the engine flywheel in between the clutch pieces and the input damper! The flywheel gets its own picture over in the crankshaft and pistons diagram, and that one doesn't show the 1-way clutch.



It also is not my understanding that the sprag clutch does anything to change the nomogram of the transmission. All of the familiar relationships between the speeds of the engine, MG1, and MG2 have to still hold. At high forward speeds without the engine turning, MG1 still has to do some pretty high reverse revs. If they have raised the road speed they allow with the engine stopped, they must have raised the limit on MG1 revs, as a separate refinement from the sprag clutch.

What the sprag clutch does is let them go further and use MG1 in that situation, to contribute more torque. If the sprag clutch weren't there, that would only spin the engine around backwards, a waste of energy (never mind how well the engine tolerates spinning backwards). But with the sprag clutch, the flywheel digs in then and won't budge, so the MG1 power acting against it has to be contributed to the transaxle output.

But if you add the spraggy teeth and 1-way bit on a car that didn't have them, the programming in the power management control ECU still won't know it is able to apply MG1 torque then without the engine spinning backwards, so it's still never going to try.

 

I'm certain I need to read more to correct my own understanding of it, but thanks for this post!

 

The trick is that the logic in the ECU is going to be different based on the presence or absence of said clutch. Re-read the last paragraph of @ChapmanF's post 31.

 

Interesting if true; would mean the programming in it knows how to roll with either a spragged or spragless engine, and would need some way of determining which one it's got, maybe from when the VIN is programmed in, or through communication with some other ECU in the car that knows.

Or did you compare the right ECUs? There's one called the transmission control ECU, whose one and only job is to slide in and out the hunk of metal that stops things when you're parked. (At least that's what it's called in Gen 3.) The hybrid vehicle control ECU is the one that really conducts the powertrain orchestra.

From what I'm seeing, the hybrid vehicle control ECU can be 89981-47780 or -47830 in a 2017 Prime, but -47557, -47576, -47B00, or -47B10 in the non-Prime (depending on whether the non-Prime is a ZVW50 or ZVW51, and I haven't kept up with what's the difference between those).


HEV CONTROL COMPUTER. 2017 Toyota Prius Prime | Toyota Parts Center Online



HEV CONTROL COMPUTER. 2017 Toyota Prius | Toyota Parts Center Online