brake question - 2017+ Chrysler Pacifica Minivan Forums
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post #1 of 14 (permalink) Old 07-03-2019, 02:04 PM Thread Starter
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brake question

I know it has regenerative braking, but at what point are the break pads used? The power / recharge gauge on the left doesn't say, so I was curious if the needle was half way or or all the way down did that mean it was using more than just regenerative braking to slow the car down. Or, maybe it always uses the break pads. I don't really know.
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post #2 of 14 (permalink) Old 07-03-2019, 04:36 PM
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Below 10mph and above 60% brake pedal effort (approximately) blends to friction braking.

If your slowing at a steady deceleration and your regen kW starts dropping off then its handing over to friction. Same as when your regen meter maxes out and you demand more braking.

So whenever your slowing and not gaining electrical charge its using friction brakes.

If case you havent seen this

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post #3 of 14 (permalink) Old 07-03-2019, 08:19 PM
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If your slowing at a steady deceleration and your regen kW starts dropping off then its handing over to friction.
You sure about that? There's more kinetic energy to convert back to potential energy between 50 to 40mph than there is from 20 to 10mph.

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post #4 of 14 (permalink) Old 07-03-2019, 09:06 PM
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You sure about that? There's more kinetic energy to convert back to potential energy between 50 to 40mph than there is from 20 to 10mph.
You need to use your common-sense here.. there are many factors.

If your still slowing and your not generating nearly any electricity then your slowing using friction. Try it - Target a specific kW regen value like 10kW and maintain it and you’ll experience what I’m talking about.

For a true understanding, test drive an i3.

It regens to a stop; then you’ll understand how much energy is still available at these lower speeds..

If you want specific function description of the braking system and the many factors involved, refer to this Tech Authority document.. but note it does define that regen is “not active below the minimun regen speed”..

https://www.dropbox.com/s/iydk8w455j...ption.pdf?dl=0

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Last edited by m0ebius604; 07-03-2019 at 09:25 PM.
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post #5 of 14 (permalink) Old 07-04-2019, 11:53 AM
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You need to use your common-sense here.. there are many factors.

If your still slowing and your not generating nearly any electricity then your slowing using friction. Try it - Target a specific kW regen value like 10kW and maintain it and you’ll experience what I’m talking about.
Oh, it's common sense alright. And a simple understanding of Newtonian physics. When you say "If your slowing at a steady deceleration and your regen kW starts dropping off then its handing over to friction," I assume you're meaning you believe it's the friction brakes. I'm simply saying that it's not accurate to say that there's the same potential energy available, as you slow at a steady deceleration. That's just physics. Of course there's less kinetic energy converted to potential energy. That doesn't mean the conventional brakes have engaged.

Put your van in L. Watch the display as you take your foot off the accelerator. You'll return more energy to the battery when slowing between 50 and 40 than you will between 30 and 20. That's without touching the brake pedal. It's simple physics. There isn't as much kinetic energy to recapture. It doesn't mean the conventional brakes have engaged.

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post #6 of 14 (permalink) Old 07-04-2019, 12:38 PM
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Originally Posted by RC Mike View Post
Oh, it's common sense alright. And a simple understanding of Newtonian physics. When you say "If your slowing at a steady deceleration and your regen kW starts dropping off then its handing over to friction," I assume you're meaning you believe it's the friction brakes. I'm simply saying that it's not accurate to say that there's the same potential energy available, as you slow at a steady deceleration. That's just physics. Of course there's less kinetic energy converted to potential energy. That doesn't mean the conventional brakes have engaged.

Put your van in L. Watch the display as you take your foot off the accelerator. You'll return more energy to the battery when slowing between 50 and 40 than you will between 30 and 20. That's without touching the brake pedal. It's simple physics. There isn't as much kinetic energy to recapture. It doesn't mean the conventional brakes have engaged.
Sigh, so much for common sense.

Do you think this is what the Op is asking? I’m sure they want to get into a broad and technical, math intense discussion over the whens and when-nots of regen..

There is a point when the HCP discontinues regen. That is the handover point.

Its 10mph, and above the max regen capability. Simple.

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Last edited by m0ebius604; 07-04-2019 at 12:41 PM.
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post #7 of 14 (permalink) Old 07-04-2019, 01:23 PM
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Are you having a bad day or something?

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post #8 of 14 (permalink) Old 07-04-2019, 05:54 PM
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Originally Posted by Emedlin View Post
I know it has regenerative braking, but at what point are the break pads used? The power / recharge gauge on the left doesn't say, so I was curious if the needle was half way or or all the way down did that mean it was using more than just regenerative braking to slow the car down. Or, maybe it always uses the break pads. I don't really know.
I think it always uses the brake pads at some point to come to a complete stop. But using the pads at such low speeds probably won’t wear them down very fast. My brother-in-law has had a hybrid for over ten years and he’s never had the brake pads replaced. I think if you go easy on them they will probably last the life of the car.

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post #9 of 14 (permalink) Old 07-04-2019, 06:20 PM
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You sure about that? There's more kinetic energy to convert back to potential energy between 50 to 40mph than there is from 20 to 10mph.
I just checked and found that the relationship between speed and kinetic energy is exponential. A vehicle going twice the speed of another has four times the kinetic energy.

So, naturally, in a steady deceleration the energy generated by regenerative braking will drop off pretty quickly as you slow down. Most likely the more pedal pressure you use to stop the earlier the mechanical brakes will start to fade in.

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post #10 of 14 (permalink) Old 07-04-2019, 07:46 PM
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Originally Posted by RC Mike View Post
Oh, it's common sense alright. And a simple understanding of Newtonian physics. When you say "If your slowing at a steady deceleration and your regen kW starts dropping off then its handing over to friction," I assume you're meaning you believe it's the friction brakes. I'm simply saying that it's not accurate to say that there's the same potential energy available, as you slow at a steady deceleration. That's just physics. Of course there's less kinetic energy converted to potential energy. That doesn't mean the conventional brakes have engaged.

Put your van in L. Watch the display as you take your foot off the accelerator. You'll return more energy to the battery when slowing between 50 and 40 than you will between 30 and 20. That's without touching the brake pedal. It's simple physics. There isn't as much kinetic energy to recapture. It doesn't mean the conventional brakes have engaged.
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Originally Posted by PacDave View Post
I just checked and found that the relationship between speed and kinetic energy is exponential. A vehicle going twice the speed of another has four times the kinetic energy.

So, naturally, in a steady deceleration the energy generated by regenerative braking will drop off pretty quickly as you slow down. Most likely the more pedal pressure you use to stop the earlier the mechanical brakes will start to fade in.
Both of your are absolutely correct..

But peak available energy isn't alway the most useful. It is better to harvest energy at a lower linear value over a longer time than to generate peak loads - You have the entire area under the exponential curve that you can opt to use.

20 sec of 20kW = 400kJ
3 sec of 80kW = 240kJ

But this question wasn't the question asked. This is what our common sense should dictate.

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