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Re: Regen and brake lights

Posted: Thu Jun 03, 2010 3:26 pm
by LEAFer
Bicster wrote:We'll find out how the regen works soon enough!

Not soon enough for me :cry: getting "antsy" already :)

Re: Regen and brake lights

Posted: Thu Jun 03, 2010 3:42 pm
by planet4ever
garygid wrote: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.

I think you are going to need a different example. I'd be willing to bet my $99 deposit that if you leave Lake Tahoe (say near the casinos) with a full battery you will never need to dump regen power on a trip to Sacramento, even though you start at elevation 6250 and end at elevation 50.

My reasoning? In the first place, you have a 1000 foot climb out of Lake Tahoe before you start going downhill. That (and the maybe 15-20 miles involved) is going to knock your battery charge down quite a ways. Second, I doubt if regen going down a hill can ever recover more than half the energy needed to get up the hill, and there is quite a bit of up and down between Tahoe and Sacramento. Third, that's a 100 mile trip, and I'm confident you would make it because of the elevation change, but I think you will have no more than 10-15% charge left when you get there.

Re: Regen and brake lights

Posted: Thu Jun 03, 2010 5:03 pm
by Jimmydreams
Bicster wrote:On any downhill grade a car will increase in speed if allowed to "coast."



Which is desirable, depending on the circumstances.

For instance, I'm on I5 in my Leaf doing 63mph while everyone around me is doing 70+ (this is California, 70 is probably a low guess!) I start down a long hill in 'coast' and top out at 70mpg. That extra speed is then transferred to the next hill since the 7mph advantage was free. Now, someone smarter than myself would have to determine if a 1/4mile hill in coast (and gaining 7mph) is a savings when applied to the next hill OR of regening down that 1/4mile hill at 63mph and then applying that gained energy on the next hill is more beneficial when it comes to total distance available in the battery pack.
;)

Re: Regen and brake lights

Posted: Thu Jun 03, 2010 6:17 pm
by EVDRIVER
People are looking at the regen issue with blinders on because all situations are different. Adjustable regen solves all the needs if implemented properly, the big issue is auto makers don't have a good system for brake only regen yet do to the blend of mechanical and electrical braking. Having too little regen "available" of pedal and attempting to compensate with greater regen on braking will be a poor experience as it will be abrupt. That is why is is usually wasted to the brake pads for a better user experience with less efficiency. Nissan will loose efficiency to make the car more seamless and to acceptable at first and future models will likely have more adjustment options or better regen braking implementations. They have the "eco" mode that gives more regen off pedal but less acceleration performance, that was a dumb choice limiting the engine output and they will find out why soon enough. What about those that enjoy the driving performance, if they want that they then get less regen, something they need even more to recapture the loss but it is only available on "Econ" where people need it less because they are usually driving slower. Typical mainstream marketing think. I can't wait to see the hacks on the first EVs.

Re: Regen and brake lights

Posted: Thu Jun 03, 2010 6:45 pm
by efusco
"Coast" is pretty vague and generally is thought to mean no accelerator and the car slowing slowly b/c of typical transmission drag or programmed regen in hybrids/evs.

"Free Wheeling" is probably the best term for "coasting" with no intentional or added drag beyond wind resistance and internal resistance of the wheels/bearings, etc.

With the Prius we often refer to coasting with slight pressure on the pedal to eliminate the induced regenerative drag as "Gliding"--that's a term that would work for a Tesla like system where there is heavy regen with absent pedal pressure, but with moderate pressure you can eliminate the regen.

With terminology defined it's a bit easier to carry on a proper discussion.

To that point, I actually like the Rav4EV system (which I've gotten to drive once). Most regen is controlled via the brake pedal. There is mild regen to simulate a "normal" coast when one's foot is completely off the accelerator. But there is a small button on the shifter you can push that puts you into a true no-regen Free Wheeling state.

As Daniel pointed out, with the Prius, finding that 'glide' sweet spot can be tricky and I'll often use neutral to simulate the same thing the little button on the Rav4EV does. It's not ideal, but it works.

Re: Regen and brake lights

Posted: Thu Jun 03, 2010 7:17 pm
by garygid
EVD...,
At least one "auto maker" (Toyota) knows how to blend braking and Regen on one pedal.

About other "auto makers", I do not know.

Re: Regen and brake lights

Posted: Thu Jun 03, 2010 7:40 pm
by EVDRIVER
garygid wrote:EVD...,
At least one "auto maker" (Toyota) knows how to blend braking and Regen on one pedal.

About other "auto makers", I do not know.



Not is you are hitting the brake pads while the pack is not full. It is not too difficult to make it seamless at the expense of efficiency loss. If brakes were fully electronic this would be easy.

Re: Regen and brake lights

Posted: Thu Jun 03, 2010 8:11 pm
by garygid
1. The pack can be empty, but the Regen current at the car's maximum, and you still need the mechanical brakes, especially when driving in heavy freeway traffic.

2. I believe that the Prius's mechanical brakes ARE electrically-controlled hydraulics, with mechanical-hydraulic backups. Yes, a quite complex system that seems to work well.

Re: Regen and brake lights

Posted: Thu Jun 03, 2010 9:26 pm
by EVDRIVER
garygid wrote:1. The pack can be empty, but the Regen current at the car's maximum, and you still need the mechanical brakes, especially when driving in heavy freeway traffic.

2. I believe that the Prius's mechanical brakes ARE electrically-controlled hydraulics, with mechanical-hydraulic backups. Yes, a quite complex system that seems to work well.



Of course you need brakes. I hope we can stop comparing hybrids to EVs unless nissan can replicate an advanced braking system that maximizes regen on brake, but based on their recent comments it seems they have not. I would venture that Toyota has more expertise here, in many areas.

Re: Regen and brake lights

Posted: Fri Jun 04, 2010 4:16 am
by LTLFTcomposite
EVDRIVER wrote:I would venture that Toyota has more expertise here, in many areas.


And perhaps a bunch of patents?