How strong is the drivetrain?

The Prius E-CVT is more or less like a differencial gearing mechanism. There are threads dedicated to reported failures in I and IIgens, which in personally I didn't catch any pattern or reason...Good to say is: very few have failed, and IIIgen has been improved further, skipping the chain. Here in Europe every 60k Km has an inspection to the oil level to be done.

 

I changed the transmission oil at 5,000 miles and had it tested. There was evidence of small manufacturing debris that hopefully were flushed with the first change. I'm planning a second change at 20,000 miles as part of my on-going transmission oil studies.

Bob Wilson

 

There is coolant (aka ATF) in the iCVT drive train, isn't there?
So if there is one, then there will be heat generated.

Considering heat is one major factor that can lead to premature transmission failure, I am curious any 2010 owner had installed ATF cooler?

ps: Another thread on tranny cooler.

 

Let's just say the maintenance schedule booklet does not have an entry for it. We change the fluid anyway as a cheap insurance.

There isn't really a transmission in the Prius. Just like series hybrid or an EV, the electric motor move the car from -25 mph backward to +112 mph forward.

 

It appears to need a cooler about as much as the center differential on a conventional car needs a cooler, which is to say not at all. Don't waste any time worrying about it.

 

Offtopic, Richard, but I'm loving the Shamen reference above your avatar.

 

There is cooling on the transaxle - the inverter coolant path goes through the inverter then down through the transaxle to the radiator and back to the reservoir. Unlike the engine coolant pump, which is temperature-controlled, the inverter pump runs continuously at a constant rate (at least, on Gen 2 a constant rate - there was some talk of it being variable on Gen 3).

I believe only the MG2 side is cooled. One of the changes for Gen 3 is that the MG1 windings are now housed in a plastic case:



which I think is something to do with the windings being immersed in the transaxle lubricating fluid. (That's the Gen 2 MG1 on the left and Gen 3 on the right.)

 

x2. I follow Toyota's recommendations.

 

Let's do some 'back of the envelope' power analysis.

The power that flows through the transaxle takes two paths:

• 72% - via power split device to mechanical gears. Use 2% loss per gear stage so 2% from the power split device of 72%.
• 28% - via electrical by-pass, assume 2% loss from generator and 2% loss from motor, round to 5% loss of 28%
• 2% per final stage - assume three gears including the differential

So adding everything together:

1.44% ~= 72% * 2% :: PDS mechanical loss
1.44% ~= 28% * 5% :: electrical bypass loss
6.00% ~= 3 * 2% :: gear stage loss (in series, the amount of power decreases per stage)
-------
8.9% ~= estimated energy loss all paths

745 W ~= 1 hp
25 hp -> 70 mph, flat land
18,625 W ~= power applied to wheels
1,660 W ~= transmission heat load​

So you have an inverter coolant loop and radiator with a pump. You also have the aluminum case surrounded on all sides by air flow. Off hand, it is hard to see a thermal problem. But of course, if you're planning to run at maximum ICE power, the only power rate that can be sustained, the power goes to 98 hp ~= 73,010 W. The heat load goes to ~6,500 W. Here is your worst case thermal problem but not the worst case temperature problem.

Roughly half of that heat comes from MG1 and MG2 stators, ~3,250 W. The heat generated has to reach the surface of the coils before it can be removed. Meanwhile, the center of the stators are going to get pretty warm. In contrast, the gear losses are somewhat in contact with a small, amount of oil. But after all, it is your car.

GOOD LUCK!
Bob Wilson

ps. These are rough numbers and folks are invited to rework for more precision.

 

I would say this first approach is correct.
Rough figures are good enough to illustrate, not to study. 500W more or less doesn't really matter...

For sure MG1 and MG2 are designed to work in a warm/hot environment or full power. If not, we would have had a tragic failure rate since I gen...
Most of electric motors are air cooled, and with a fan to provide forced convection.