Hybrid Car – More Fun with Less Gas

Engine Braking - Page 3

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Posted by Michelle Steiner on September 20, 2005, 3:55 am

It is true for the 2004 and 2005 Prius.

It doesn't work incorrectly when in B.  It doesn't work in B because
when you shift to B, it turns off cruise control.

Stop Mad Cowboy Disease:  Impeach the son of a Bush.

Posted by Calidous on September 20, 2005, 5:06 am

Although I've yet to use B, that makes perfect sense to me because I'd only
use it to lose speed.  Why would I use it to maintain speed?

Posted by dbs__usenet on September 23, 2005, 10:31 pm
Imagine, if you will, the 7,000 foot sumit.  You have 25 miles of gentle
downgrade ahead, with the road mostly allowing 55 to 65 mph curves.

You set the cruise control at 60 and put the gear in 'D' and find yourself
going into a corner at 75 MPH.

You change to 'B', slow down to 60 and engage the cruise.  Every few
miles you hit a 45 MPH curve and tap the brakes.  After the curve you
tap resume to get back to 60 MPH.

At the end of the 25 mile slope you have a solid screen of 100MPG bars and
you were safe the whole time.

That's when I use cruise and 'B'.


Posted by Paul Missman on October 3, 2005, 9:58 pm
I have a slightly different take on engine braking.

I've seen some folks say that it is a useless feature, and some who have
found it quite useful.

My take is this:

I own a 2 seat, Piper Tomahawk aircraft that I land on a 2000 foot runway in
Virginia.  On landing, I cross the threshold at about 67 MPH, always stop in
2000 feet, and have had practically no brake wear.  I've made hundreds of
landings, and, as far as I can tell, my brake pads will last for many years
to come before needing replacement.  The secret is that, whenever possible,
I make use of full flaps on landing.  In addition to creating more lift at
landing speeds, they also add significant drag to the airflow.  I also use
the body of the plane, in nose up attitude, to create even more drag.  Thus,
I use air drag to do almost all of my braking for me, and only use the
actual brakes at the very end, just before turning off of the runway.

I view the engine brake in the Prius the same way I view my landing
technique.  The more I can stay off the brake pedal, the longer those pads
and rotors will last.  I realize that the brake pedal is, in part,
regenerative.  However, I cannot tell exactly when it stops being purely
regenerative and when it begins to be mainly pads and rotors.  With the
engine brake, I know it is fully regenerative, and no brake pad is being
wasted.  Thus, I've begun to use the engine brake often and early, to bleed
off some of the energy before having to apply the brake.  In some instances,
you can bleed off all of the energy, and not have to hit the brake at all.
This should make for much longer brake life, at the slight expense more back
pressure being applied to the gears in the transmission.

It would be nice if Toyota could add to the energy screen a dual bar graph,
which would display the percentage of braking done by regeneration and the
percentage being done by the brake pads while braking.  This would certainly
help in extending brake life.


Posted by Bill on October 3, 2005, 11:28 pm

Hi Paul,

From what I've read, engine braking will reduce economy.  There was a great
article posted in another Prius forum giving the charge parameters for light
and moderate brake pressure that made a believer out of this private pilot.
Maybe someone who frequents this group has a link to it.

The key, I believe, is to simply let up on the gas a little earlier or use
steady, light-to-moderate pressure.  Yes, it would be nice to have a light
or tone that indicated friction braking.  Just today I used hard pressure to
stop my Prius and they really squealed as I peeled away the rust that had
accumulated from not being used for several months.


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