Hybrid Car – More Fun with Less Gas

"Downshifting"

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Posted by Stan and Dee Bringer on May 10, 2005, 12:22 am
 
I had the opportunity to "test drive" a Prius the other day and was greatly
impressed with the lack of traffic noise inside the closed car.  What a
tight fitting car!  The acceleration is more than satisfactory and the
instruments on the dashboard

I taught Driver Education and Driver Training for thirty-five years at a
school near my home.  I always taught my students to "shift down" when they
are going down a long hill.  Near my home is a freeway off ramp that has the
reputation of being the steepest downgrade of all the freeway off ramps in
California.

I didn't have the opportunity to drive the Prius down that off ramp, and I
forgot to ask the sales person.  What is the procedure when driving down a
long, steep off ramp.  It sppears you can't "shift down!"  Does the
regenerative braking provide extra braking action on the downgrade?  Are the
brakes on the Prius sufficiently large and cooled to prevent overheating or
glazing?

Stan



Posted by Earle Jones on May 10, 2005, 12:52 am
 


Stan:  There is a way to "downshift" -- just put the joystick in
"B", which stands for "braking" (I think.)  This fires up the
Internal Combustion Engine (ICE) and provides engine braking --
actually, it feels very much like downshifting in a regular
transmission.

In "D-Drive", you get some braking downhill from regeneration, but
not sufficient to protect your brakes on a long, steep section.

earle
*
(Happy owner of my '05, now with 6K miles.)

Posted by Michael Pardee on May 10, 2005, 3:38 am
 
Beyond my direct experience, but... others on the Yahoo Prius group reported
checking their brakes after a long steep downhill and found them still cold.
Regenerative braking should be enough for several miles of repeated braking
or prolonged deceleration. You can tell when the battery is too full to
absorb more by checking the battery icon on the "energy" display. Our 2002
fills after about 2000 feet of descent - I don't know about the second
generation models. Once the battery displays full, use of "B" will reduce
wear on the brakes. Before that it just wastes energy that could be
partially reclaimed.

I agree this is very counter-intuitive to us geezers. I downshift our Volvo
dozens of times a day to reduce brake wear in this hilly town and have to
remind myself the brake is the best way to slow the Prius except on very
long low speed descents. (At freeway speed the aerodynamic drag is enough to
keep the battery from filling on any decline I've encountered on the West
Coast.)

Mike



Posted by richard schumacher on May 10, 2005, 3:16 am
 

When you find yourself riding the brakes when going downhill, put it in
"B".  This increases engine braking (the engine spins without fuel or
spark, using kinetic energy to pump air; "jake brakes" without the
noise).  Don't forget to put it back in "D" at the bottom of the hill or
fuel economy will suffer.

Posted by Bill on May 10, 2005, 3:27 am
 

I was under the impression that constant light to moderate pressure on the
Prius brake pedal governed the battery regenerative charging rate and that
"riding" the brakes going downhill improved fuel economy.  If my
understanding is correct, only steady, heavy pressure would engage the
mechanical brakes causing them to overheat.



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