I have never seen an ICE RPM in the range under ~1000 either -- thus the reason for the last paragraph in my last post. I suspect that there would be problems with lubrication, if nothing more severe - and there are lots of possibilities. The values I stated were entirely theoretical (and stated as such), if it could be done.

I agree with you regarding the open circuit. As we agreed, the physical wiring from the ECU to the MGs does not disconnect, and any relay or other electronic switching for electrical disconnection is the same one normally used by the ECU control circuits. Without the ECU powered up, the saturation voltages induced by the MG would be uncontrolled and unloaded, and could possibly become high enough to defeat the switching circuitry.

However, I also still accept the argeument for the MG1 overspeed. Even if we accept a 50% overspeed as allowable, a towing speed of 60MPH would exceed that value without the ICE turning -- This without a pressure lubrication system for bearings, any mechanism for cooling or other secondary systems.

 

[QUOTE I thought the car would put out heat and air conditioning even with the engine not running. Could be it has to be left in gear or drive for that to occur.[/QUOTE]

The ICE has to be running for the heat but not AC..............

 

According to the maintenance manual there is an electric heater that is used in ECO mode to provide some heat without running the ICE.

 

While driving about with heat on and you stop for light or sign, MPG gauge shoots up to 0. Now shut off heat and ICE shuts off and needle drops down to elec mode. This engine is like any other water cooled engine and needs to circulate HOT water through the heater core to provide warmth. Just finished 5650 mile trip thru high country in AZ, NV and NM and saw this happen many times as I tried to get better MPG at low speeds. I live in Fl and my MPG dropped while out west in the cold weather. Using heater in city driving was one cause. Climbing to 8000 ft. altitudes was another.

 

I find that if I turn on ECO the ICE will also shut off.

I was wrong about ECO, ECO will inhibit the electric heater, increase the engine off time, and prohibit BI-LEVEL mode during AUTO operation (according to the manual). It is also cancelled during DEF or FOOT DEF mode or the MAX HOT temperature setting.

The maintenance manual discusses the electric heater:
The heater is described somewhat differently in another section of the manual:
So it looks like you should get some heat immediately in cold weather with ECO off, but I've never noticed it.

There is also an electric heater water pump:

 

FastMover — I think we're basically in agreement then. I have some difficulty with your MG1 speed numbers, however. I checked them in my formula, and find that my numbers are significantly lower than yours. Perhaps there's something wrong with my formula, but I don't think so. I took into account all the gear ratios as specified in the Toyota Manual, and I think that I've got the tire circumference correct too. If I use my formula, I find the following correspondence between your and my numbers:

1. You say -10 816 rpm. I say -8266 rpm.
2. You say 1200 rpm. I say 4102 rpm.
3. You say -8600 rpm. I say -6494 rpm.
4. You say 600 rpm. I say ~0 rpm.
5. You say -4980 rpm. I say -2894 rpm.

What's going on? Why are we in disagreement?

Also, I believe that the speed limit for the TCH's MGs is well above the 6500 rpm you quote, which was for the Prius. I believe that they're rated at at least 10 000 rpm. For example, in the TCH, MG2 has a second planetary-gear set (with one shaft pinned) acting as a coaxial reduction gear between MG2 and the ring-gear of the PSD. [In the Prius, MG2 runs at the ring-gear speed, what I call Nr.] In consequence, MG2 spins much faster in the TCH than in the Prius. In the Table I gave in "Heretical Mode," I calculated MG2's speed at the car's governor-limited top speed of 185 km/h (~115 miles per hour) to be 12 938 rpm. And, were the ICE not spinning, MG1 would then be spinning at -13 574 rpm. I have read somewhere the belief that the MGs can withstand 14 000 rpm. It seems to me that this may indeed be the case! [Of course, Toyota would not recommend that such speeds be attained frequently!]

Stan

 

I'm not sure it's really unsafe as most cars these days are perfectly capable of stopping quickly without the aid of engine braking. Many European cars in the 50's & 60's like Auto Union, DKW, Saab and Wartburg that were powered by 3 cyl 2 stroke engines were fitted with a "free wheel" mode that disengaged the clutch when you lifted off the gas. It was to prevent NON oil injected 2 cycle engines from running out of lubricant as you descended a steep hill and not to save gas.
My question would be, could coasting for prolonged periods cause the tranny to overheat as in early automatics where the pump would not work when in neutral?

 

My family had both the 2 Stroke Saab and the 4 cylinder...both with free-wheeling. Whether it was intended to save gas..I don't know but if you drove it right...it did save gas. 35-40 mpg in 1969 or so driving in upstate NY including the hills of the Adirondacks and New England. Since gas was about 30 Cents a gallon....that was sweet.

 

Andy, speaking from a previous Saturn SL1 owner perspective, the answer, IMHO, would be to have the eCVT lubricated much like the Saturn that is so popular with Motorhome owners over the past decade, and that is to lubricate the tranny by movement of the front wheel(s), not the engine turning. That's why you see so many Saturn vehicles being towed behind motorhomes. The automatic x-mission is simply put in neutral, and you can tow it indefinitely w/o fear of lube starvage.

It just seems so simple. Saturn stopped including this feature for four years, and then resumed again in 2007 I believe. They realized their mistake, when motorhome owners who didn't want to purchase manual x-mission tow vehicles, started buying other brands.

 

FastMover — Look at the attached SAE paper on the second-generation Prius (2004, THS II). On pages 5 and 6 you'll find reference to the increase in the allowable maximum MG1 speed from 6500 to 10 000 rpm. The MG2 speed didn't increase in this redesign since there's still no reduction gear between MG2 and the ring-gear. In the TCH there is such a reduction gear, and I believe that both MG1 and MG2 are rated at 10 000 rpm or higher. As I said, I believe that I've seen 14 000 rpm mentioned somewhere. And from my calculations, this seems to be about right. Note that the top speed of the TCH is considerably higher than that of the 2004 Prius too.

AndyB — I believe, like KenE, that the TCH's transaxle is lubricated by an oil pump driven by its output shaft, as well as by splash lubrication. So it would be quite safe, from a lubrication point of view, to tow it in 'N' with the ICE stationary.

Stan

P.S. (2008-03-10): To comply with SAE copyright, I have removed the paper that I had originally attached to this post. It is SAE Technical Paper # 2004-01-0064 "Development of New-Generation Hybrid System THS II — Drastic Improvement of Power Performance and Fuel Economy" by Koichiro Muta, Makoto Yamazaki, and Junji Tokieda of Toyota. The sentences I referred to are:

1. "Improvements such as rotor strength have increased the rpm range from 6,500 (in the normal condition) to 10,000 rpm."
2. "... an increase in the maximum revolution of the generator from 6,500 to 10,000 rpm ..."

P.P.S. (2008-03-10): The maximum ratings of both MG1 and MG2 in the TCH are indeed 14 000 rpm, as I commented above. See the Oak Ridge National Laboratory Report referenced by buyhevs in the thread "Camry Hybrid Transaxle National Labs Report," and my subsequent post #9 in that thread.