Prius less efficient at highway speed than two-mode hybrids?

ken1784 · 06-15-2006, 10:05 PM

<div class='quotetop'>QUOTE(usbseawolf2000 @ Jun 11 2006, 04:36 AM) [snapback]269256[/snapback]</div>

Quote:

HSD used in GS450h and LS600h (eCVT L110) has two speed (3.9:1 - 1.9:1) variable reduction gearset to reduce the size of the electic motors, improve torque at low speed and reduce ICE RPM at high speed! This implementation was evolved for high powered HSD. It has nothing to do with inefficiency of HSD on the highway.
[/b]

Also, the speed ranges are different between Prius(max 170km/h) and GS 450h(max 250km/h).
The variable reduction gearset is used to meet wider speed range.

Ken@Japan

hobbit · 06-15-2006, 10:20 PM

ISTR that the GS450h et al were getting a dual-planetary system,
but maybe I'm thinking about something else. There are already such
systems on the road, such as in some hybrid buses; see the slides at
http://www.engin.umd.umich.edu/vi/w4_works.../Miller_W04.pdf
.
Also, go read Graham Davies' pages and look up "heretical mode".
With the single-planetary HSD as it is in the Prius, the faster you
want to cruise at lower RPM, the more that MG1 has to be forced to
spin *backwards* by zoobs from MG2. That's a less efficient
electrical hop than we might want, but we have no choice there
because the tradeoff is letting engine RPM creep up which increases
consumption for relatively little proplusive gain.
.
Changing to a more "overdrive" mechanical ratio is the way to
fix the problem.
.
_H*

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06-15-2006, 10:20 PM	#12
hobbit Senior Member Join Date: Mar 2005 Location: Bahstahn Posts: 3,625 My Car: Model: Package: Thanks: 0 Thanked 216 Times in 118 Posts Friends: 0	ISTR that the GS450h et al were getting a dual-planetary system, but maybe I'm thinking about something else. There are already such systems on the road, such as in some hybrid buses; see the slides at http://www.engin.umd.umich.edu/vi/w4_works.../Miller_W04.pdf . Also, go read Graham Davies' pages and look up "heretical mode". With the single-planetary HSD as it is in the Prius, the faster you want to cruise at lower RPM, the more that MG1 has to be forced to spin backwards by zoobs from MG2. That's a less efficient electrical hop than we might want, but we have no choice there because the tradeoff is letting engine RPM creep up which increases consumption for relatively little proplusive gain. . Changing to a more "overdrive" mechanical ratio is the way to fix the problem. . _H*