Hi,
Quote:
Originally Posted by orange4boy
. . .
About coasting in neutral... Transaxle damage? Max speeds? What are the dangers? How does the oil pump work? Is there some body of knowledge on this?
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The following model showing the relationship between ICE, MG1, and MG2 rpm:
Toyota Prius - Power Split Device
The critical speed is 42 mph, 67 km/h. At or above 67 km/h, the control laws will keep the engine running. Regardless of vehicle speed, it is always OK to put it in "N" as long as the engine is running. So if I'm on a road where I want maximum glide, slip it into "N" and keep on rolling.
Below 67 km/h, the engine is optional, the hybrid operating range. Again, below 67 km/h, it is always OK to put it in "N". But if the engine is off and the car put in "N," it can no longer start the engine. The potential risk is putting the car in "N" on a down grade and having the vehicle speed increase over 67 km/h with the engine off.
As MG1 spins faster and faster, it generates a higher and higher voltage. There is a Dept. of Energy paper (ORNL/TM-2004/247) that maps the voltage vs rpm curve for the NHW20 (2004-2009) Prius showing what happens. The current hypothesis is that with the ICE not turning, the MG1 rpm above 67 km/h can generate voltages so high that the inverter could be at risk from over voltage. The nomographs suggests the following MG1 redlines:
- 6,500 rpm - NHW11 (2001-03) Prius
- 10,000 rpm - NHW20 (2004-09) Prius
My NHW11 has been up to at least 50 mph, 80 km/h, with the engine off and going down hill. Hobbit has done similar overspeed experiments with his NHW20. So the over speed failure isn't 'instant' but neither of us have a great interest in testing to find the absolute MG1 limit. In my case, if going down a grade and my speed increases to 42 mph or higher, I shift the car in "D" to get the engine started and back to "N" but that is how I drive.
The transaxle pump is driven by the engine. However, it is not a pressure based, lubrication system in the traditional sense. The gears and axles are OK with this. The only time significant stresses might occur is when the engine is at full power and then the pump will be turning.
One of the best collections of Prius knowledge is "Prius Technical Stuff," the Yahoogroup. It has message archives going back to 2000, the first NHW11 Prius in North America. Even now, there is a hard core group of Prius technophiles who hang there sharing experiments and addressing rebuilder problems. The files section includes photos, graphs, papers, and other studies ... an unusually rich source. It is the network version of Ecomodder specific for the Prius. FYI, it is 'first post moderated,' which keeps down the the SPAM.
Bob Wilson