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Posted by Michael Pardee on February 2, 2009, 12:46 pm

FWIW, a few regulars in the Yahoo! Prius_Technical_Stuff forum have reported
seeing (on a Scanguage) the ICE not turning at speeds somewhat above 42 mph
and MG1 above the putative redline, even in a stock Classic Prius. There has
been speculation the redline may be for the inverter when MG1 is being used
for a motor rather than for a generator.

The 6500 rpm limit was for the Classic (NHW11), while in the NHW20 the limit
is supposed to be 10,000 rpm. Says JerryW: "MG1 would not be exceeding its
rev range until well over 70mph. I don't think we know why the ICE still
starts up at 42mph now. I don't, anyway.."


Posted by Peter Granzeau on February 2, 2009, 9:24 pm

It seems that individual Prius act differently.  Mine almost always runs
the ICE any time the battery status indicator shows blue bars, and will
only cruise on battery if the indicator is showing green.  I have
managed about 40 mph on battery only when the load was light (gentle
downhill slope); straight and level (or as near as it gets--I live in
tidewater country, and there are still often gentle grades on streets
and highways.)

Posted by Mr. G on February 3, 2009, 4:30 am
 (pgranzeau@cox.net) says...

The ECU in the Prius will 'learn' your individual driving habits and
modify its parameters accordingly.  I don't know enough about exactly
how it does that to explain the situation you described, though possibly
based on your driving habits there are often situations where the
battery will discharge rapidly, so it attempts to top it off whenever
possible.  In my '07 I have no problem driving for long stretches with
the ICE off.  My MFD battery display is often showing blue, though
rarely goes below half the bars showing.

Posted by Tomes on February 3, 2009, 10:40 pm
Mine too.  Which is why I really wish that it would use the electrics moreso
than it does now.

Posted by Mr. G on January 29, 2009, 10:47 pm
 T. Johnson (djohnson@isomedia.com) says...

The ICE and electric motors are not just multiple inputs to the drive
system; the way it is designed, the speed of one directly affects the
speed of another.

The planetary gear system is basically the same thing as the
differential on a rear-wheel drive car.  In that scenario, the input to
the differential is the drive shaft, the the two outputs are the right
and left drive wheels.  Turning the driveshaft causes both wheels to
move forward, but if one wheel is slowed down, the other will speed up,
so that their combined RPM is equal for any given input RPM.

In the synergy drive, the driveshaft is now the output shaft, one wheel
is replaced by MG2, and the other side has the ICE & MG1.  With this
arrangement, the speed of the output shaft is the COMBINED speed of the
ICE/MG1 + MG2.

To make things simple for illustration, assume the planetary gears have
a 1:1 ratio. (the numbers are purely fictitious, and are only to
illustrate the concept.)  To get a 100 RPM output speed, the ICE/MG1 and
MG2 must both be running at 100 RPM.  If the ICE/MG1 is increased to 200
RPM, then MG2 must be at 50 RPM.  If MG2 is at 200 RPM, then the ICE/MG1
would reduce to 50 RPM.  In actual use, the ICE/MG1 is spun at its most
efficient speed, and MG2 spins at whatever speed is required to give the
desired output speed.  This includes spinning backwards if the required
output speed is slow, but the ICE/MG1 wants to run at a high RPM, such
as going slowly up a steep hill.

When the ICE/MG1 is not moving, then MG2 must spin much faster to
compensate, since it's providing all the RPM.

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