Regen and brake lights

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garygid said:
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.
 
Bicster said:
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.
;)
 
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.
 
"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.
 
garygid said:
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.
 
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.
 
garygid said:
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.
 
LTLFTcomposite said:
EVDRIVER said:
I would venture that Toyota has more expertise here, in many areas.

And perhaps a bunch of patents?

Do the auto majors have cross-patent agreements ? Players in many major industries do - so that they don't spend time fighting each other in courts. That also keeps new comers from ever competing effectively.
 
I'm pretty sure that Nissan has licensed Toyota's Prius Hybrid Synergy Drive system and is using it in the Nissan Altima Hybrid (you're kind of driving a Toyota Prius!). And Toyota has licensed Nissan's CVT (not sure if the Prius uses that one).
 
LEAFer said:
And Toyota has licensed Nissan's CVT (not sure if the Prius uses that one).
The Prius does not have a CVT in any conventional sense of the term. It has a patent on the planetary gear system used in the transaxle (though not w/o dispute).
 
Don't know whether this was quoted earlier.

http://www.easyecar.com/electric-vehicle-test/nissan-leaf-first-drive/

It has a 80 kW motor that gives a VERY powerful acceleration. The regeneration I only very little when you take the foot of the accelerator and it goes to maximum when you apply the brake.
 
I asked Nissan about this - and they're not talking, yet. So at this point it's just speculation.

John said:
Does the regenerative braking increase proportionately depending on how much pressure is applied to the brake pedal?
Nissan said:
Dear John,

Thank you for taking the time to personally contact us about your interest in the Nissan LEAF.

Details about regenerative braking are not released at this time. When more details are available we will update on the website http://www.NissanUSA.com.

We appreciate your time, and encourage you to share our contact details with friends and family. For your convenience, we can be reached:

By return email, through our website at http://www.nissanusa.com, or by phone at 877-664-2738.

We’re here to serve you from 7:00 a.m. to 7:00 p.m. (CST) Monday through Friday and 8:00 a.m. to 4:30 p.m. (CST) on Saturday

Sincerely,

Nissan Electric Vehicle Customer Support

***This email message is provided in response to your recent inquiry to Leaf Customer support so should not be considered unsolicited commercial email.
 
garygid said:
For me, no variable Regen on the brake pedal ... means "no sale".

In that case will you be replying back to Nissan with another "Dear John" letter? :lol:

Notice that in that letter only one substitution is required:

Details about what you asked about are not released at this time.
 
daniel said:
The only thing the Prius does wrong is putting a small amount of regen on the accelerator pedal to mimick an automatic. This results in making it very difficult to coast when you want to, since you have to find exactly the right pedal position. Separating the functions means you can go faster when you want to, go slower when you want to, and coast when you want to. With hard braking (regen) on the accelerator pedal, coasting is very difficult.
Much as I respect you and your opinions Daniel, I have to disagree. I LIKE the 'dead band' glide in the Prius, I just wish it was easier to find and hold. I use it all the time as I'm sure many other Prius owners do as well. If someone ahead starts to slow, I don't want to have to take my foot off the accelerator and move it to the brake for light 'slow down'. When traffic allows me to leave reasonable gaps, I don't touch the brake pedal until I need to physically stop the car at a light or stop sign. So I *want* a '3 position' accelerator pedal
  • foot off = Light regen
  • light pressure = glide
  • more pressure = regular acceleration
Just make the 'glide' range about 1/2" 'deep'
 
planet4ever said:
Using minus energy is a lot better than no energy.
Not necessarily. Using NO energy means you aren't losing kinetic energy that you have paid for. Using 'minus' regen means losses going into and out of the battery. The best possible is maintaining speed or slowing very gradually due to rolling resistance AND using NO energy. 'Glide' a quarter mile to the red light rather than using fuel to travel 1/8th mile then regen to slow the next 1/8th. You will never recover as much energy regening the last half as you used to travel the first half (presumig no significant downhill slope of course).
 
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