Engine Braking

How many of you use the Engine Braking feature? Do you find it useful?

Reply to
Doug
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I use it only on long downhills; it beats using the brakes. Sometimes, it's not enough and I have to use the brakes as well.

Using it instead of normal braking in normal conditions reduces gas mileage.

Reply to
Michelle Steiner

Only on descents of more than about 1000 ft elevation or so. Check your Energy screen and when the battery gets to "full" it is better to rely on engine braking instead of the regenerative braking. As Michelle states, engine braking reduces regeneration.

Mike

Reply to
Michael Pardee

Actually I said it reduces gas mileage.

Reply to
Michelle Steiner

I've not used it in the seven months I've owned my Prius and doubt I ever will in MN. Next time I pass through CO on my way to AZ I probably will.

Reply to
Ingenuous

It's real nice when you are exiting a mountain range. It will slow the car quite well on a 4 or 5 % slope. I kick in the cruise control and let it take care of business. If the engine braking is not enough for real steep downgrades you do have to tap the brakes.

Reply to
dbs__usenet

  • Remember that Cruise Control doesn't work when you are in "B" mode.

earle

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Reply to
Earle Jones

I didn't know that! It makes sense, though, and could be an important consideration when somebody says their cruise control doesn't work.

Mike

Reply to
Michael Pardee

While I have heard that several times, I've proven it incorrect in my 2002 Prius. I've shifted to 'B' and set cruise while coming down through the cascade mountain range in southern Oregon, and watched it keep the speed close to where I wanted it. I've also seen it hold the speed as I went back up small inclines. I've done this multiple times. It's not a fluke.

Is it just the newer models that don't use the cruise when in 'B'? Is it the act of shifting to B that turns off the cruise? Is it the fact that you typically tend to hit the brakes occasionally when going downhill, thus disconnecting the cruise?

There is no intuitive reason for cruise to work incorrectly when in 'B'. If the engine braking slows you too much, it speeds up the engine. If you are going too fast it increases the drag.

It does not keep the speed as close to target when going downhill in 'B' as it does in 'D' on fairly flat land. It might go 5 MPH over now and again.

Daniel

Reply to
dbs__usenet

I was confused as to why my '05 would not lock into cruise. Turns out it was in "B." Maybe something changed the way they thought about its operation?

B~

Reply to
B. Peg

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.

Reply to
Michelle Steiner

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?

Reply to
Calidous

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'.

Daniel

Reply to
dbs__usenet

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.

Paul

Reply to
Paul Missman

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.

Bill

Reply to
Bill

I'm no expert, but I've come to believe the braking is almost entirely regenerative under normal conditions. Some people have the Coastal Electronics friction brake indicator light and they can tell you more about it than I can. We know it reverts to friction brakes at low speed, when the stopping called for is harder than the regen can do, when the battery is "full" and when going over bumpy surfaces. Otherwise, I don't think the pads get much use.

Using the B setting will definitely burn off energy, but it will do that whether it needs to be burned off or not.

Mike

Reply to
Michael Pardee

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