Coasting or Braking?

Well, the original question was really "Which would be more advantageous mpg-wise?" and not "How do I get the most regen?", even though he started with the regen question.

That said, I would suggest that coasting, regardless of it's regen ability, would probably provide you with better MPG. My reasoning for this, is that if you have to actively use the brakes to stop the vehicle, then you consumed fuel/battery power for longer prior to braking than you would have if you started coasting earlier inorder to coast to a stop without applying the brakes.

However, coasting to stop is not always, and in fact often not practical. At least not in traffic.

 

I've really learned a lot from this thread. Even though I'm more than halfway through the owner's manual, I've seen no explanation of any of this regenerative stuff. In fact, if it weren't for this forum, I wouldn't even know about it (the dealer didn't mention anything).

While I have several questions floating around in my head, the main one is: Where can I learn what I should be trying to accomplish in terms of the interplay between regenerative braking, coasting, the "B" gear, regenerating the battery vs. maxing out MPG, etc? Is there one explanatory article?

I know I can just drive it and not worry about it... but all this seems rather fun and interesting to me.

Thanks!

 

Suggest reading the threads
http://priuschat.com/forums/-vt10359.html
http://priusonline.com/viewtopic.php?p=43865
.
After installing a battery current meter and a
prototype brake-pressure indicator, it all becomes
clear. Regen current is limited to 100A maximum, and
you're more likely to top that with moderate pressure at higher
speeds. As regen current is exceeded, the REAR brakes
begin to receive hydraulic pressure first, to balance the car.
The whine you hear under regen braking isn't really the
motors, it's the inverter doing heavy PWM switching to
regulate battery charge current.
.
Links to some of my instrumentation are in the
priusonline thread above. Also see
http://techno-fandom.org/~hobbit/cars/imeter/
for the battery-current hack.
.
_H*

 

There is no doubt that braking creates a higher RATE of charge, but the real question is the CUMULATIVE power "saved" over the braking distance.

In other words, does the slow regen from coasting, accumulated over the longer period of time, exceed the higher-rate braking recharge over a shorter time?

Put another way, which puts more power back into the battery by the time you stop?

Sounds like a new variant on a common bumper sticker is coming...

I BRAKE FOR REGEN

 

it is assumed that you are using the car to go somewhere so acceleration at some point will be necessary and the greatest mileage is gained by not slowing down NO MATTER WHAT THE METHOD. so will coasting provide more regen or will controlled braking provide the greatest overall charge in a given distance. well that is a good question but why do you want to know is what i am wondering.

the best way to increase the mileage is too maintain a steady speed. you want to do that without hitting anyone. so coast if you can, use your brakes if you must. accelerating back to your cruising speed with more than negate the gains from regen.

as for my personal experience, coasting gets me the great mileage as opposed to good mileage. you might not think so, but in the summer time, i think 50 mpg SUCKS!! cant even begin to tell you how disappointed i would be if that is what i was averaging. but its not the coasting that helps as much as learning to anticipate your speed needs. i rarely drive on single lane roads so i dont give a rats nice person what anyone thinks of my driving, i will start coasting 5 blocks from a light that i know i will have to stop at in hopes that i will never have to hit the brakes. light timing is part of it, but you also have to look at how many cars are lined up at the light and how long its gonna take for them to get moving also.

so stop if you have to, but lowering your speed a few mph and creating a greater following distance will get your much better results

 

Drafting works better than coasting. Just did a 60 miles trip this afternoon on Rt78 and Rt287 in NJ behind a big rig. Did not get too too close, about 5 car lengths and staying in his draft the entire trip. With A/C running in my '02 I was able to get 61.5 mpg. Not too bad!

 

maybe i'm reading it wrong, but do you mean coasting by feathering or switching to neutral? or coasting by letting off the gas but letting the regen system still work without hitting the brakes?

if the latter i'd say as long as the friction brakes don't kick in, it shouldn't make that much of a difference. but maybe someone who knows for sure should comment

 

My general thoughts:

Anything that avoids a full stop works best. If you can coast slowly and prevent a stop, you will get better mileage than applying light brake pressure, coming to a full stop, and startinging again.

If you know you MUST stop (stop sign, let's say), use light/moderate brake pressure to maximize regen. Plus the people behind you won't be upset about your coasting instead of braking to a stop stign.

 

"maybe i'm reading it wrong, but do you mean coasting by feathering or switching to neutral? or coasting by letting off the gas but letting the regen system still work without hitting the brakes?"

I meant by simply letting up on the gas and letting regen and friction slow the car.

 

Assuming you have to brake. Best is to coast and then brake. Never slow with foot off the accelerator. Just don't coast so much you need the friction brakes.

This is clear from the braking efficiency curve posted at:

http://www.vassfamily.net/ToyotaPrius/

 

Bingo! I was going to post his website. So, go neutral, whether actually, or virtually by feathering, until you reach the distance to where you need to begin stopping at the most optimum rate determined by Atilla, which is about 20 seconds to go from 40MPH to 0.