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DeaneG
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Re: Regen and brake lights

Wed Jun 02, 2010 7:53 pm

Jimmydreams wrote:Personally, I'd like zero pressure on gas pedal = 100% coast (no regen)
Pressure on brake pedal = regen (more pressure, more regen)

I live in some hilly terrain....I'd like to be able to completely coast down the hills at speed using virtually zero power. If there was regen involved, I'd constantly be switching back and forth.


I would think you'd like to collect regenerative power while maintaining speed down those hills, rather than coasting? Unless the hills are shallow enough that you never accumulate too much speed without braking now.
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evnow
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Re: Regen and brake lights

Wed Jun 02, 2010 8:39 pm

DeaneG wrote:I would think you'd like to collect regenerative power while maintaining speed down those hills, rather than coasting? Unless the hills are shallow enough that you never accumulate too much speed without braking now.


maintaining speed = coasting. Atleast thats how I'm using it.
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planet4ever
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Re: Regen and brake lights

Thu Jun 03, 2010 1:24 am

Jimmydreams wrote:Personally, I'd like zero pressure on gas pedal = 100% coast (no regen)
Pressure on brake pedal = regen (more pressure, more regen)

I live in some hilly terrain....I'd like to be able to completely coast down the hills at speed using virtually zero power. If there was regen involved, I'd constantly be switching back and forth.

Well I certainly hope regen is involved driving up and down hills. Using minus energy is a lot better than no energy. And I, too, don't want to be switching back and forth between pedals while doing it. But I'm having trouble making sense of your position. Are you saying you want your foot on the go-pedal going uphill and on the stop-pedal going down? Isn't that switching back and forth? Me, I want my foot on the go-pedal going either up or down. And I want enough regen to keep the car from speeding up on steep hills unless I push the pedal to tell it to do so.

After 55 years of knowing I should never hit the brake going around a corner downhill, there is no way I could bring myself to do it, even if I was coasting way too fast.

OK, OK, I guess if you've got one o' them newfangled traction thingamabobs that rule don't apply no more. But it's deeply ingrained in my brain cells, and probably the brain cells of about fifty million other "seasoned" drivers.
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garygid
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Re: Regen and brake lights

Thu Jun 03, 2010 8:22 am

There is NO fixed value of Regen that will work for all downslopes and speeds. So, to be useful in "holding back" the car, the Regen amount must be variable.

Typiccally, there are only two variable controls that are familiar, the go-faster and go-slower. One can split the Regen control between them, with zero to "light" on the go-faster, and "light" to "full" on the go-slower.

Then, "coasting" is not easily available, but might be accomplished by holding the go-faster down a little.

Or, the Regen (a going-slower function) can be entirely controlled with the go-slower. Then, low-drag coasting would be done with the foot off the pedals, or even "barely touching" either pedal. This is not a "keep the same speed forever" mode, the tire and wind drag would gradually slow the car.

On greater-than-gentle slopes, the "little" regen will be insufficient, so one will need to use the go-slower. Occasionally (perhaps not in "flat-land") there will be steeper grades that will require more than the "full" regen, so the mechanical brakes will be needed ... all the way down the "possibly-long" grade, perhaps 1 to 50 miles.

Note: This means a LOT of brake heating! Much MORE than a typical (down-shiftable) car would require. Hopefully, the EV brake designers realize this, and provide brakes that have ZERO heat-fade.

When anticipating stopping, it is best to have one's foot already on the go-slower.

Having the "light" level of Regen adjustable (or switchable) from "light" to "zero" would make the controls satisfy both camps.

This can be a simple Software setting, no extra physical buttons or controls are needed.

During every "anticipated" slowing or stopping sequence, there is the possibility to save energy by not using any, by coasting. Slowing with Regen might only be 50% energy effective. However, when judging when more braking is needed, I want my foot in the safest place, already on the go-slower. In traffic, the cars in front of me can decide to brake suddenly. Also, as soon as I decide that de-acceleration is necessary, I want my car's stop-lights to go on, to give warning to the guy behind me.

Rear-end accidents are the most common here in freeway traffic, and you can stop OK, but giving extra warning to the driver behind ... might save YOUR life, and at least save your LEAF.
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Re: Regen and brake lights

Thu Jun 03, 2010 8:59 am

kballs wrote:... parallel hybrids have done it wrong (with their complicated jerky/uneven brake blending systems that are universally noted as an annoyance).

Universally noted as an annoyance??? I drive a 2004 Prius and you CANNOT tell where the regen braking ends and the friction braking begins. A few (VERY few) people have characterized the Prius brakes as "grabby," but they are a tiny minority. NOT "universal."

Toyota manages the combination of regen and friction braking on the brake pedal excellently. If they eliminated braking from the accelerator pedal entirely, and eliminated vehicle creep when the feet are off the pedals, it would be perfect.

"Coasting" to me does not mean steady speed. It means no power to the car, and no braking. The car rolls freely, subject only to rolling resistance and gravity.

Putting all the regen on the accelerator pedal (Tesla style) requires a lot more skill from the driver. Maybe that's okay for a high-performance roadster, but not for a family sedan.

But putting light or no regen on the accelerator, and none on the brake pedal, means you mostly use the brake pads, and this is wasteful, and for long steep downhills would be dangerous. So the brake pedal should use all regen until regen is no longer adequate and the brake pads become necessary. (Toyota style.)
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Re: Regen and brake lights

Thu Jun 03, 2010 9:06 am

garygid wrote:On greater-than-gentle slopes, the "little" regen will be insufficient, so one will need to use the go-slower. Occasionally (perhaps not in "flat-land") there will be steeper grades that will require more than the "full" regen, so the mechanical brakes will be needed ... all the way down the "possibly-long" grade, perhaps 1 to 50 miles.

Note: This means a LOT of brake heating! Much MORE than a typical (down-shiftable) car would require. Hopefully, the EV brake designers realize this, and provide brakes that have ZERO heat-fade.

That's why the very strong regen on the Tesla is sufficient on (probably) all but the steepest hills to maintain a constant speed without touching either pedal ... the cruise-control controls the go-faster pedal (although I don't know if it actually "moves" the pedal, since all it needs to control is the current into or from the motor). For the LEAF it would be great while the driver is using cruise-control that it maximizes the regen on a down-hill to avoid use of the friction brakes. The fact that the driver is using cruise-control should be a "flag" to the software to allow maximum (more than normal) regen. Brake heating therefore would not be a concern.
(The maximum regen on the Tesla runs between 80-90A. At nominal 375V for the battery, this means 30-34kW ! (Think "charging the battery" !) Most of the time, that's for short durations, of course, but on a long steep hill (think Tahoe to Sacramento) it is for a significant benefit.)

Edit: before somebody jumps in ... ok, Tahoe to Sacramento is not one constant downhill, and it also has uphills, but you get the idea.
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garygid
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Re: Regen and brake lights

Thu Jun 03, 2010 9:14 am

If the battery gets "full" (quite possible) and there is no place to "dump" 35 kW of power, the Regen is basically useless.

So, on the long trip home from Tahoe, the mechanical brakes will get ... VERY hot!

So, yes, brake heating is an important, even vital, safety issue.
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Re: Regen and brake lights

Thu Jun 03, 2010 9:26 am

Of course ... I guess the Tesla driver is expected to be smart enough to NOT leave Tahoe with a full battery ! :D But, good point, thanks for pointing that out.
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Jimmydreams
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Re: Regen and brake lights

Thu Jun 03, 2010 11:26 am

DeaneG wrote:
Jimmydreams wrote:Personally, I'd like zero pressure on gas pedal = 100% coast (no regen)
Pressure on brake pedal = regen (more pressure, more regen)

I live in some hilly terrain....I'd like to be able to completely coast down the hills at speed using virtually zero power. If there was regen involved, I'd constantly be switching back and forth.


I would think you'd like to collect regenerative power while maintaining speed down those hills, rather than coasting? Unless the hills are shallow enough that you never accumulate too much speed without braking now.


That's exactly what I'm saying. Most hills around here would cause ANY amount of regen to slow the vehicle, while 100% coast would be perfect. I agree on steeper hills you want some regen to keep the speed from increasing. If the regen is adjustable, I'm a happy camper. If it's preset and I have to work around it, I'll be slightly less so.
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Re: Regen and brake lights

Thu Jun 03, 2010 11:53 am

On any downhill grade a car will increase in speed if allowed to "coast."

They can program the regen to maintain speed. That would not be coasting.

I think Nissan's design goal is to have the car drive just like any car with an automatic transmission, minus the shifts. There is forward creep when the brake is released and the car is stationary, for example.

We'll find out how the regen works soon enough!
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