CVT being used in EV mode?

If the car is moving, in any mode, something in the 'transmission' or transaxle is being used.

Unlike an ICE, electric motors have a continuous RPM operating range all the way down to zero, so the raw need for a 'transmission' is reduced or eliminated. But with the gasoline engine still sitting there and connected, it gets used anyway.

 

Easy way to remember it: the transmission is where the electric motors are.

 

I believe that the sun gear is connected to the MG1, while the planet carrier is connected to the engine. Might be wrong though. Either way, the e-CVT (not CVT) is always moving when the vehicle is moving. The Prime can be hauled forward by MG2 only (the Power Split Device "outer ring") or combination of MG2 and MG1 ("outer ring" and "sun").

 

Actually, on the Prime there is a one-way clutch that lets MG1 add power at low speeds, IIRC.

 

The Prius transmission (or rather 'transaxle', because the final drive and differential are also inside it), when viewed as a whole, which functionally includes the electronics inside the box above it, is absolutely a "continuously variable transmission", or CVT. You can call it an e-CVT if for some reason you want to emphasize the way it works, but there is no point to saying "not CVT", because there is no functional attribute of a CVT that the Prius transmission doesn't provide.

"Not CVT"-style comments boil down to it not being the kind of CVT that is built with cones and pushbelts and so on. Which, sure, it isn't, but that's like saying a gas kitchen range isn't a kitchen range because it isn't electric.

 

I believe the clutch is in place to allow MG1 to help MG2 when extra power is needed. But I'm no technical expert on the matter...

EDIT: This might help a bit:

 

Uhmmm... the ICE is connected to the planet-gear carrier, not the sun gear.

 

Please pardon my ignorance here... I just bought a new 2020 Prime last wee and am trying to learn.
Have some questions if you would be kind enough to answer.
> Prime has e-CVT, not the conventional CVTwith a steel belt and a pair of converters or cones. Correct?
> Is there transmission or transaxle oil to be replaced? If so, is there a drain plug and fill hole?
> Are there clutch/friction plates that would wear out?
Thanks in advance.

 

You could say it that way, if it's important to you. The CVT in a Prius is not the kind of CVT that is made with cones and a pushbelt, or the kind of CVT made with perpendicular disks. There are many kinds of CVT that it is not. It is the kind of CVT that is made with two electric motors, an inverter, and a planetary gear set. You can call it "e-CVT" if you want and you're in the kind of conversation where anybody cares how the CVT works inside. (Although, in that kind of conversation, maybe it's more interesting to just describe how it works inside; what does "e-CVT" really tell you?).

There are plugs for draining and filling. It is factory filled with an oil that only serves to lubricate things and not degrade the electrical insulation of the motors. It is not pumped through torque converters or clutch packs or anything like that. It lives the life of a manual tranny oil, more or less. People might change it after several tens of thousands of miles, or a small number of times in the car's life, more or less.

There is one dry-plate torque limiter (like a clutch that is never disengaged), really just there to protect the engine and gear train from very rough bounces. It isn't expected to be a wear item in the normal life of the car. It can be, if, for example, the car is driven around with a severe misfire, that kind of thing.

 

I am still reminded of the AAMCO commercial where they have an exploded view of an automatic transmission, and they brag that they can maintain all 800 of its parts. Versus the Prius transaxle, with about a dozen parts that are permanently connected to each other, and really nothing to maintain.

Concerning clutches in the Prime, there is also a one-way clutch that allows MG-1 to move the car without the gasoline engine being turned backwards. But there are no pressure plates or anything like that to wear out in this sort of device. This is specific to the Prime, and is not in the non-plugin Prius models.