Best Deceleration Rate?

Hi metalnut,

Welcome to PriusChat . . . fellow Sacramentan! Thank for purchasing a Prius and helping Sacramento maintain its standing as the #2 spot in the USA for Prii per capita! Maybe we can catch the Bay Area.

http://priuschat.com/index.php?s=&showtopi...ndpost&p=254213

The correct answer to your question is: For maximum fuel efficiency, it is best not to brake or regen.

It is best to glide as much as you can (or as much as you can stand, or the drivers behind you can stand :angry: ) and come to as slow and steady of a stop as you can with minimum use of of the brakes or regen.

The sooner you let off the gas and electric propulsion and go into glide mode (no arrows on the MFD), the less energy you will waste in your travels from point A to B.

Only a small percent of the regeneration energy makes it into the batteries. And then, even more energy is wasted converting that battery voltage back to wheel motion. The Prius will never recapture all of that energy, so it is best not to waste it on braking and regenerating in the first place.

If you must step on the brake pedal to stop . . . and most of us do . . . “a gentle, but firm push on the brake pedal†is best for efficient regen braking.

This link will take you to the information you are looking for . . . if you must use the brakes.

http://vassfamily.net/ToyotaPrius/CAN/brindex.html

 

Wayne Brown did extensive testing to answer this question. You can find the relevant posts in the yahoo 2004-prius group. I think his handle is mwbueno.

I seem to remember that the HV battery can take up to 20 Amps. A bit of math would tell you the maximum rate that kinetic energy that can be taken up.

Or, if you are the qualitative type: as slow as smart driving allows
As Patrick says, don't brake for regen sake, but if you know you have to brake, start early.

Lastly, I do not brake with constant pressure. If traffic allows, I start *very* gently, and from about 20 mph and down, gently increase the brake pressure to fairly firm by the time I have stopped. I think I am gaining three things this way: one, at higher speeds the car bleeds off much more kinetic energy per mph/sec drop, and I don't want to exceed the battery's Amp capacity; two, there is a slight jolt at very low speeds when the wheel brakes kick in that I find annoying, and this technique blurs it; and lastly, the rotors have a tendency to rust from lack of use, so I try to heat them up below 10 mph or so, when regen is pretty much nil anyway.

 

<div class='quotetop'>QUOTE(metalnut @ Aug 6 2006, 01:15 AM) [snapback]298555[/snapback]</div>

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I ran across a web site ( http://privatenrg.com/#100kBrakePads ) where a guy had the personal experience of the SURPRISINGLY SMALL AMOUNT of front brake pad wear.

His words, "At 100,520 miles, I literally could not measure any wear on these pads with my metal mm ruler. I know there has to be some wear but, it appears that I will have to remove the pads and use a pair of calipers to measure such a small amount. This is pretty incredible!"

This tells me that the regenerative brake system conserves pads like the dickens! It feels like you are actually using up brake pads, when stepping on the pedal. But apparently you are mostly - - efficiently recharging the battery!

 

Frank, you happened upon the web site on one of the most brilliant and knowledgeable Prius owners in the US: Wayne Brown. His website is a cornucopia of things Prius. His yahoo handle, as I wrote above, is mwbueno.

A modest bow before entering his domain would be reasonable

 

I think I am way over my head here until I read back more of this and check out the other website...

So....if I am coasting down a long hill which will end most likely in a stop sign or red light....do I keep coasting even though I am picking up speed and don't have another hill to climb when I reach the bottom??

I hit the top at around 20-30 mph...then pick up lots of speech on way down...so I am way into 40s...(above slimit!)...and begin breaking toward the end? I thought that the coasting was giving me better mpg, and that it was better to brake nearer the end as needed...or should I be braking little bits on the way down?

Certainly, if I have another hill to climb and can use some of the speed generated to assist the coming climb. These are all local hills in my neighborhood, but many are long and down or short and steep down...and reverse is true on upside. ....and

I only drive short distances at a time in my area...5-15 minutes....

terri

 

I think the advice provided by efusco is probably very good. I would add one other thing. I believe around 7 or 8 mph the disc brakes kick in so I usually try to keep my braking and speed above 10mph if I am descending down a hill. I live near a hill that has little traffic so I can experiment with speed, but unfortunately I don't have CAN--VIEWER in my 2006 Prius.

<div class='quotetop'>QUOTE(efusco @ Aug 6 2006, 07:01 PM) [snapback]298812[/snapback]</div>

 

<div class='quotetop'>QUOTE(efusco @ Aug 6 2006, 07:01 PM) [snapback]298812[/snapback]</div>

But, if that downhill run happens to be a 55 mile, 4,775 foot decline (Touloumne Meadows to the Yosemite Valley floor) . . . lightly riding the brakes, gliding, and EVing in the appropriate places has its benefits too.


http://priuschat.com/index.php?s=&showtopi...ndpost&p=276244
.

 

If you're at 50 mph and seeing arrows battery --> motor --> wheels,
that's "warp-stealth". Learn how to get into that state and hold
it, because it's an important contributor to good MPG in the mid-
speed range.
.
The best way to regulate regen braking force is being able to see
your battery current, via can-view or something else that can pull
it digitally off the bus, or an analog rig tapped into the battery
box current sensor. I find that 50 - 60 amps seems fairly optimal
too -- healthy regen, but not going all the way up to 100A to avoid
a little more ohmic heating in the pack and wires, etc.
.
_H*

 

Thanks, Evan!!

Your answer pretty much covered the way I have been using the "coasting" to go downhill more and more.

Some of my hills are shorter and steeper and I know that if I have too much speed going into them, I will pick up way too much speed for my sedate wooded community...LOL...like high 40s.

So...I have been slowing slightly with easy braking as I near a hill and then coast (all green arrows going down) braking slightly as I pick up too much speed.

I do try to watch the lights ahead, now, too and sometimes I am able to stay in coast mode until the light changes and keep on going.

We really have a very hilly area near the northern shore of Long Island...especially blocks from the beach where I live.

Also, I noticed since yesterday, that I started out on my second tank of gas at 60 mpg...because I could actually get into "stealth" mode (Is that the same as "deadscreen"...i.e. no arrows) and I could use the downhills to coast. Short trip home, only 5-7 minutes...then I got to my own neighborhood and had some steep ups and quick downs so...

by the time I got home I was at 41 mpg...

This morning I had to dash out to doctor (although I am now trying to bunch my errands so the ICE stays warmed up) and I had mostly "climbing...although to look at the road, one wouldn't think so...steady but even pressure to even keep at 30-35 mph.

By time I got to the doctor, I had dropped to 31 mpg....BUT

on the way home, the hills worked for me, and when I shut the car off, I had two green cars on the energy consumption screen (is 4 the max?)
and my mpt was near 42 mpg again...so I will learn my neighborhood.

It definitely seems to my advantage though to not accelerate "briskly" up the hills as I have seen mentioned elsewhere...as nice steady, not slow acceleration works better....

Also, I can deadscreen under 30 mph....some of the time I am all electric (all yellow arrows)...and can deadscreen for short spurts.

Can I read out the braking amps??? Don't know if that's something extra?

I do use the lighter braking, though, on the way down hills to avoid excessive speed build-up especially when I am facing a sure stop and because it would take me way over speed limit in my area.

I was going to take the car into Toyota because my first tank averaged out at 31 mpg calculated, 32.8 on MFD. But I did need to have better mpg toward fill-up, in order to bring that first part of the tank that was at 25 mpg up to the 31-32 range.

Definitely with the hills, a rather even, steady pacing, using the downhill slopes and a nice steady climb to get to place where I can go into stealthmode for even a little bit, seems to be what will work for me.

I will never be driving this car for any distance on a highway....or rarely......

Thanks again, Evan....

I am learning so much here at the forums.

terri