[RED]

I know when I take my foot off the gas pedal at anything over ~7 mph, the MFD shows the arrows charging the battery and I feel a slight drag on the vehicle. This is obviously the regenerative braking occurring, without actually putting ones foot on the brake pedal. My question is around how to get the most charge out of a "braking session" by actually using the brakes.

If I press down slightly on the brake pedal, am I charging the battery faster than if I was just coasting with my foot off the brake pedal? Is there an optimum speed to keep below (or above) while applying the brake, say down a fairly steep hill? I own a 2006, and seem to get a slightly different brake feeling right around ~41mph.

I’m just trying to understand if while coasting down a hill, I should just not touch the brake pedal until I get near the stop sign, or press lightly on the brakes all the way down the hill and try to time my stop with the stop sign ahead.

In other words, is there a point at which you can step on the brake without turning any energy into heat to the rotors/drums and have the regenerative braking work harder? Or is regenerative braking binary (just full on, or full off)?

As always, thanks for you inputs. This board is great!

Cheers!
-Ray

 

[efusco]

Lots of "depends" here....but let me try to help.

Depending upon your speed regeneration of 'coasting'--foot off brake and accelerator-- results in ~15-20 amps of charging.

Moderate to firm braking, depending upon speed of travel, can generate up to 90+ amps. The steeper the hill and faster you're going the more you can regenerate.

If you coast and wait to the very bottom there's a bit more of a chance that you'll engage the friction brakes and not get maximal charging.

OTOH, if you hit a bump while braking regeneration can cease completely and you'll get little or no charging the rest of the way to the bottom.

Help or confuse.

 

[Tideland Prius]

my thinking is that light braking will always have more regeneration than simply letting it coast. There's no way to tell if you're getting maximum regeneration without CanView scangauge

 

[DanMan32]

Atilla was able to make some measurements: http://www.vassfamily.net/ToyotaPrius/CAN/brindex.html

Best to apply slight braking, about 22 seconds to go from 45 to 5 MPH.

Other neat observations he made:
http://www.vassfamily.net/ToyotaPrius/C ... sures.html

 

[efusco]

Atilla was able to make some measurements: http://www.vassfamily.net/ToyotaPrius/CAN/brindex.html

Best to apply slight braking, about 22 seconds to go from 45 to 5 MPH.

Other neat observations he made:
http://www.vassfamily.net/ToyotaPrius/C ... sures.html

There's a problem, however, when you convert Atilla's data (also Wayne Brown found much the same thing) to real life....

They measured energy regenerated over a speed (from 40 to 5 mph), but in real life what matters more is distance.

Stay with me here...
I'm cruising down the road at 45mph and there is a stop sign 1 mile ahead that I know I have to stop for.

I know that light to moderate braking will generate the most energy and that light to moderate braking will make me stop in about 1/2 mile of distance from 45mph. Thus, I must drive *using power* 1/2 mile further down the road before I start braking.

Or, I can back off the pedal, go into a glide or allow the passive regeneration to begin slowing the car gradually over that 1 mile distance. Although my accumulated energy of regeneration will be slightly smaller, my NET energy gain is greater b/c I didn't use power to travel that extra 1/2 mile.

Now, I'm not saying that we should always start slowing down a mile away from stop signs, but if we're using the ICE or even the battery to travel closer to our intented stopping point just to get maximal regeneration then you're defeating the goal of saving as much energy as possible.

To summarize, I suggest always back off the power completely as soon as practical to do so based upon your own driving style, road conditions, and traffic flow/conditions. If you're going down hill or on a flat and want to use a slight pressure on the gas pedal to glide before braking then great, that should work to your benefit when you apply light to moderate braking pressure.

 

[TWOPWRS]

I was surprised you guys did not mention the braking mode next to the drive mode. Do any of you use it?
My concern is what is doing the braking? Is it the engine or the electric motor? I use it occasionally and it seems to work pretty well, but I wonder what exactly am I doing?
DanMan can you throw any light on this situation?

 

[efusco]

I was surprised you guys did not mention the braking mode next to the drive mode. Do any of you use it?
My concern is what is doing the braking? Is it the engine or the electric motor? I use it occasionally and it seems to work pretty well, but I wonder what exactly am I doing?
DanMan can you throw any light on this situation?

B-mode is very inefficient. Regen maxes at about 20-25 Amps, the ICE spins at about 3000+RPM to assist the slowing...wasting energy that otherwise could have been recaptured with regen braking.
If you have a very long hill to go down and don't want to use your friction brakes (which you will once battery charge is optimized/maximized at about 70-75%) then B-mode could help. I haven't used it in well over a year other than to see exactly what affects would show on CAN-view.

 

[Tideland Prius]

Atilla was able to make some measurements: http://www.vassfamily.net/ToyotaPrius/CAN/brindex.html

Best to apply slight braking, about 22 seconds to go from 45 to 5 MPH.

Other neat observations he made:
http://www.vassfamily.net/ToyotaPrius/C ... sures.html

There's a problem, however, when you convert Atilla's data (also Wayne Brown found much the same thing) to real life....

They measured energy regenerated over a speed (from 40 to 5 mph), but in real life what matters more is distance.

Stay with me here...
I'm cruising down the road at 45mph and there is a stop sign 1 mile ahead that I know I have to stop for.

I know that light to moderate braking will generate the most energy and that light to moderate braking will make me stop in about 1/2 mile of distance from 45mph. Thus, I must drive *using power* 1/2 mile further down the road before I start braking.

Or, I can back off the pedal, go into a glide or allow the passive regeneration to begin slowing the car gradually over that 1 mile distance. Although my accumulated energy of regeneration will be slightly smaller, my NET energy gain is greater b/c I didn't use power to travel that extra 1/2 mile.

Now, I'm not saying that we should always start slowing down a mile away from stop signs, but if we're using the ICE or even the battery to travel closer to our intented stopping point just to get maximal regeneration then you're defeating the goal of saving as much energy as possible.

To summarize, I suggest always back off the power completely as soon as practical to do so based upon your own driving style, road conditions, and traffic flow/conditions. If you're going down hill or on a flat and want to use a slight pressure on the gas pedal to glide before braking then great, that should work to your benefit when you apply light to moderate braking pressure.

yeah so wouldn't it be better to glide for ½ mile then do the light-moderate braking?

 

[efusco]

yeah so wouldn't it be better to glide for ½ mile then do the light-moderate braking?

That's what I do.

 

[DanMan32]

Yup, glide until you get to speed or distance that will allow for optimal braking, and reaching your target location at near 0 speed.

Now if we can tie this to NAV, with NAV containing locations where stops occur, we can have the car optimize our stop rate. There should be an option to have it optimize the acceleration rate. I believe the CC is programmed already for that though.