Brake.

Letting off the accelerator uses the 10kW motor to regenerate. Pressing the brake uses the bigger 50kW motor. I can't remember the maximum amperage that goes into the battery.

However, if you were going down a grade (10%? 15%?), you'll go from 6 to 8 bars in 30 secs at 50-60km/h at near maximum regen.


IOW, max regen regenerates quite a bit. On a flat road at 50mph, I doubt you can get up to 8 bars from 6 but you'll be fairly close.

Here's a test to see if you were regenerating or not. You'll have to do this multiple times to get a feel for it.

Brake like you normally would. When you're below 20mph, shift into B. The amount of extra drag you feel when you shift into B tells you how well you've been regenerating prior to the shift.

For example, if you were lightly brake or not even braking at all, when you shift into B below 20mph, you'll feel a significant drag as the car goes to max regen.

However, if you were braking close to the threshold, then shifting into B should result in little extra drag (you won't feel the car slowing down further).

Now he comes the second part. How do I know if I was regenerating near max or were using the friction brakes (since both would result in no extra drag when shifting into B).

Hold the brake pedal at a constant angle. When you're near 5-8mph, the friction brakes will engage and you'll feel a slight "give" as the system switches over from regen to friction braking.

If you feel that "give", you've been regenerating. If you don't feel that give, that means you were using the friction brakes all along.



Using these two techniques, you should be able to find the threshold. Just note that the type of shoe you wear will make the feel different too. I know cause I've gotten the feel of the braking in my old shoe but then it was worn and I had to use another pair of shoes and now I'm re-learning.

 

teeres always loss both mechanical and electronic, at best you'll see no more than 60% more if all is right less for conditions, gravel road, rain and such.

 

gotta stop letting Frizzy type....... sorry :?

 

Answering the original Q:

"Do I just take my foot off the accelerator and let it coast down with a very slow regeneration, or is there some loss with that method because of resistance or some other phenomenon so it is better to brake firmly and steadily?"

I would argue that, once you realize that you have to stop from a speed of 40mph or greater, it's best to employ reasonable braking rather than letting the car just coast. Consider:

1: The faster you are going, the more energy is being wasted pushing air out of the way, at least until you get down to 30-40mph.

2: OTOH, if you brake very rapidly, you may exceed the best amperage for efficient energy storage in the batteries, or even, with rapid braking, start to employ the friction brakes.

3: But, if you gently brake, you will dump more energy into the batteries and less into heating the air.

It's hard to put numbers to "reasonably braking" but maybe you know it when you feel it.

Richard

 

:roll: Looks like Frizzycat666 doesn't know how to use the capitalize function. :lol:

 

Atilla did a study and determine that a braking factor of 13 (based on CAN data regarding brake force) was optimal. I don't know however if his determination was based on max power presented to the battery which the battery may or may not store all of it, or if he was able to determine it based on what the battery actually stored.

The brake force was a bit higher than zero pedal drag.

So, optimal braking would be zero drag coast until you get to speed/distance where optimal braking rate would get you exactly where you need to stop.

B mode may set the default drag to the optimal rate, but there are other aspects of B mode, mainly how it handles ICE, that are not ideal.

http://www.vassfamily.net/ToyotaPrius/C ... sures.html

 

I think you're asking the wrong question. Or, if you're really concerned only about "regeneration" and not 'net energy' then I'd have to ask why.

Assuming your question is accurate and you only want to know about regen and net energy is not a consideration then you'd want to use the data aquired by Atilla and aim for a stopping distance such that you could maintain approximately 60amp braking. That will probably be around 1/8 mile from 50mph.

Here's the issue though.....
If you're going 50mph on a highway and want to conserve as much total energy as possible you have to look at this a slightly different way.

If you wait until 1/8th mile before your intended stopping point you'll have to expend energy all the way until that 1/8th mile mark. While your total charge going to the battery may be maximized the net energy conserved will be less than if you'd gone to a coast 1/2 mile away from your intended stopping point b/c you'll have 3/8ths of a mile less of fuel burning. So maybe you'll only be regenerating 15amps for that 1/2 mile, but you still net less energy consumed over that 1/2 mile.

I do try to aim for the 60amp braking when I'm on a long downhill and such, but I've decided that, when practical, it's much better to slow down early into either a glide or a coast than to wait until closer to my stop just so I 'get' to brake at 60amps.

 

Atilla did a study and determine that a braking factor of 13 (based on CAN data regarding brake force) was optimal. I don't know however if his determination was based on max power presented to the battery which the battery may or may not store all of it, or if he was able to determine it based on what the battery actually stored.

The brake force was a bit higher than zero pedal drag.

So, optimal braking would be zero drag coast until you get to speed/distance where optimal braking rate would get you exactly where you need to stop.

B mode may set the default drag to the optimal rate, but there are other aspects of B mode, mainly how it handles ICE, that are not ideal.

http://www.vassfamily.net/ToyotaPrius/C ... sures.html

Once again DanMan32 comes through with the exact answer I was looking for.

Looking at Atilla's chart, it would take 62 seconds to coast to a stop from 45 mph, but the amount of regenerated energy would be less than if you stopped in 22 seconds. But that corresponds to the CAN value of 17. And of course the distance to stop would be much different between coasting and braking.

You would not be expending energy before you would apply the brakes for maximum regeneration though, because you would stop accelerating and either coast or apply the brakes. The topic of "net energy" is applied if you can possibly refrain from stopping completely.

 

And another thought on what efusco said is that it may actually better to brake at CAN value 17 when you see the stoplight far enough in advance, conserve as much speed as possible, and then start accelerating again when the light turns green. I had been coasting in advance, and thus using up more distance than I had to because I thought coasting was most effective at regeneration, always trying to guess the maximum speed I could possibly maintain.

Essentially it may be better to "brake and glide" than just coast in some situations.

 

Remember that even in a 'no-arrows glide' you're still draining your battery... -6 amps at speeds below 42mph and ~-12amps at speeds higher than that (hyper-stealth/glide). And that must figure into your net energy gain/loss formula. The further you glide before you start your 60amp braking or whatever level you settle at the more energy you'll passively drain....yet you can travel much further over that distance.

It gets complicated when you start trying to split the hairs of absolute best/maximum net energy efficiency.

But the take home message, I think, is that the further away you can anticipate a stop, enter a glide, get the ICE to a zero fuel use state, then efficiently and slowly come to your stop the better.