bruceha2000
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Re: Regen and brake lights

Fri Jul 09, 2010 2:20 pm

Jimmydreams wrote: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. ;)
Clearly not necessary, you already got it right. NO way you can get as much out as you generate via regen. The only reason to regen down that hill would be if you went over the speed limit enough to get a ticket. Clearly in your scenario, you won't be passing anyone. 75 is the de facto minimum in a 65 zone in CA unless there is too much traffic.
2004 Prius - 49 MPG
No Leaf - I live in Vermont, Nissan won't sell me one

bruceha2000
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Re: Regen and brake lights

Fri Jul 09, 2010 2:27 pm

efusco wrote: I'll often use neutral to simulate the same thing the little button on the Rav4EV does. It's not ideal, but it works.
I don't think I like the Rav4EV function unless pressing on the accelerator even slightly kicks it back into 'non free wheel'. Otherwise it is no different than putting the car in N. Plus the only way to slow a little would be to move to the brake pedal. That is why I like the 'light pressure' Prius glide, ANY more pressure and you are in 'regular drive', any less and you are in minimal regen slowdown. LOTS of control with minimal foot movement (if more difficult than necessary to find and hold).
2004 Prius - 49 MPG
No Leaf - I live in Vermont, Nissan won't sell me one

bruceha2000
Posts: 25
Joined: Thu Jul 08, 2010 12:05 pm

Re: Regen and brake lights

Fri Jul 09, 2010 2:36 pm

garygid wrote:The 2010 Prius will not "coast" without careful (and tedious) feathering of the go-faster pedal.

In my mind, that is a sub-optimal "human interface" design.

I'm not sure it is an intentional design feature but an 'incidental' benefit of the power split device found by drivers and spread through the forums. It sure as heck isn't in the owners manual.

If it was intentional, I think they would have made it easier to get to and hold 'glide'.
THAT would be a good 'design feature'. It isn't pushing, it isn't retarding and the transmission is still in 'D' and it is EASY.
2004 Prius - 49 MPG
No Leaf - I live in Vermont, Nissan won't sell me one

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Jimmydreams
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Re: Regen and brake lights

Fri Jul 09, 2010 3:12 pm

bruceha2000 wrote: Clearly in your scenario, you won't be passing anyone. 75 is the de facto minimum in a 65 zone in CA unless there is too much traffic.


Only if you want it to be. I drive 5 days a week on the 5 in the far right lane doing 60-62mph, and I'm a bother ONLY to those that think the far right lane is for high-speed passing. Usually, there is a truck in front of me or someone else pacing me behind.

Try it. Just stay to the right and slow down. You'd be amazed at A) how much gas you save and B) how little you really affect the flow of traffic. :D
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Quixotix
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Joined: Mon Jul 12, 2010 1:24 pm

Re: Regen and brake lights

Tue Jul 13, 2010 6:29 pm

bruceha2000 wrote:
Jimmydreams wrote: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. ;)
Clearly not necessary, you already got it right. NO way you can get as much out as you generate via regen. The only reason to regen down that hill would be if you went over the speed limit enough to get a ticket. Clearly in your scenario, you won't be passing anyone. 75 is the de facto minimum in a 65 zone in CA unless there is too much traffic.


While I think you are right in this case bruceha2000, it is not quite that clear. Since aerodynamic drag is roughly proportional to the square of the speed, you loose more energy when you coast faster. So, while you are absolutely right when you say "NO way you can get as much out as you generate via regen." It is also true that there is NO way you can get as much out as you gain by coasting to a higher speed.

Because of the complexities of this example (not only varying speed but varying acceleration down the hill and then again up the hill) and mainly because I'm way out of practice doing dynamics problems, I'm not going to try to calculate a precise answer to this example. Instead I'll just do some simple calculations:

If you travel at 63 mph for a given distance you only use 81% as much energy to push air as you would at 70 mph (63^2 / 70^2 = .81). You could say that traveling at 70 compared to 63 is only 81% efficient.* In a roundabout way, you could compare this to the efficiency of the full regen cycle (regen and then back to power at the wheels). If the regen cycle is more efficient than 81% (not likely) then it might compare well to the extra speed method. Again, this is a really-really rough comparison, a lot more calculations would be needed before anything definite could be said.

However, one more thing: As the hill gets longer, and the speed difference increases, things move in favor of regeneration. Take 50 and 70 mph. Here 70 is only 51% as efficient as 50 mph (50^2 / 70^2 = .51). Regen might be able to beat this.

* I am ignoring rolling resistance throughout this post because: 1. It is relatively small compared to air resistance at higher speeds, and 2. It is basically linear with respect to speed.

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evnow
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Re: Regen and brake lights

Tue Jul 13, 2010 6:44 pm

Jimmydreams wrote:Try it. Just stay to the right and slow down. You'd be amazed at A) how much gas you save and B) how little you really affect the flow of traffic. :D


In a job a few years back - I was 3 exists away from office. I'd usually get on the freeway just drive @ 60 in the right most lane and exit after about 10 miles.

Frequently I'd see people who got in with me to the freeway - and drove as fast as they could using different lanes - and finally ended up just ahead or behind me at the exit.

"Hasten slowly" / "faster you go, later you reach".
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