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Discussion Starter #1
Hi Everyone. I am the owner of a RAV4 EV and a Prius, and I live near Denver, Colorado.

As far as I know I am the only person in the world to have this unique combination of vehicles and in a location such as mine. After driving a (non-plugin) hybrid for four years and a plug-in EV for a year, I have determined a few things about how the Volt needs to operate. I have mulled this over many times and realize that the Volt must have a driver-selectable mode switch to meet various conditions. The switch would have three modes, described as follows:

1. "Commute" mode. In this mode, the vehicle will drive on the battery until it is depleted, then maintain the lowest safe (non-damaging) SOC (State of Charge). The vehicle will soon be near an outlet, so there is no point in bringing up the battery. This mode also assumes that the car will not need to do anything strenuous anytime soon. This would be the default mode, the car could fall back to this everytime it is restarted.

2. "Long Trip" mode. In this mode, the vehicle will assess the current SOC. If the SOC is high, it will allow the battery to reach the happiest mid-point, either by driving on the battery alone (if the SOC is high) or by running the generator (if the SOC is low). The generator will continue to run at its most efficient opportunity while in this mode.

3. "Mountain Climb" mode. In this mode, the vehicle will take every opportunity to keep the SOC at its highest "safe" point. The generator will run vigorously to continuously supply electricity even as the battery is being drained significantly.

There are several issues that arise if these modes are not manually selectable.

The first scenario:
I live 40 miles from the base of the I-70 Westbound climb up to the Continental Divide at Eisenhower tunnel. If I drive the first 40 miles to the base of the mountain on electric, the car will then struggle to climb the mountain and the battery's SOC will become dangerously (to the health of the battery) low. This happens in my Prius, in fact, I killed the battery in my Prius, and at under three years and 29,000 miles, am one of the only people ever to have their battery replaced. The problem is that the Prius doesn't aggresively charge the battery during a mountain climb, because it doesn't know you are climbing a mountain. The Prius could easily run its generator continuously to resolve this, but if it ran this way all the time, it would kill the MPG's when back on the flats down in Denver.

The next scenario:
Let's suppose my commute is about 50 miles and my battery ran out at 40 miles. The generator kicks in and gets me home, but what should the SOC be when I get there? It should be as low as tolerable, since I'm heading towards my 240V 50A plug. However, maintaining even mildly low SOC is not healthy for a long trip, which I might suddenly need to do some time, nor is running the generator for only three minutes a day, since it wouldn't be warmed up and would be very inefficient and dirty, not to mention bad for the engine.

Yet another even worse scenario:
Let's suppose I live a the top of the mountain, and can regen all the way down to work in the morning. (Like people here in Denver do). I might need the car to charge only until halfway, then regen down the mountain until the SOC is full, then drive around Denver's front range on battery until the SOC is low, then drive up the mountain again. This is essentially an impossible situation for a fully automatic REEV like the Volt. It begs for manual control of the modes.

I worry that I am the only person in the world who has a full understanding of these scenarios because of my unique proximity to the mountains and my experience with the RAV4 EV and Prius. I'm looking for some deep thinkers to come up with an algorithm that would solve these scenarios with a fully automatic implementation, because I don't see one. If there is anybody on this site who has some thoughts on this, please share them.

Basically, how do you: Use as little fuel under all scenarios but still maintain a healthy middle point of SOC so that the battery doesn't get overly stressed and the car is able to climb a mountain with ease? Keep in mind that the air at 11,000 feet is very thin and there is less power coming out of the engine, forcing the car to rely on the battery more, or drop to a snail's pace. My RAV4 EV is very, very good at mountain climbing. It actually gets more powerful as the air gets thinner. My Prius is abysmal at climbing the mountains, but can go much further than 100 miles at a time.

The mode selector switch seems to be the only solution I can come up with.

Nate
 

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Very good thoughts!

If the manual control was there, it would remove the necessity of designing in increased ICE output to keep up with the most unusual driving circumstances. The car could be power sized for "normal" usage instead of that one case of the unusual. That would save a few production bucks and ultimately consumer bucks.

"My RAV4 EV is very, very good at mountain climbing. It actually gets more powerful as the air gets thinner."
Nater! How did you get a RAV4e and how well does it work in the cold? People just flatly say that the EV1 with NiMH couldn't work in northern states. Does the power of NiMH hold up during cold weather? Thanks!

I would like the regen adjustable so that I can select no regen when the foot is lifted from the accelerator. Why? Because regen is not 100% efficient, if I can time the lights and coast a lot the drive becomes more energy efficient and a longer electric range is possible. Regen should variably come on when the brake peddle is touched and intensify when slowly depressed. Some people may prefer the ICE feel of immediate regen when the foot is lifted from the accelerator. GM make it adjustable from a menu. Put in your defaults but let the owner/driver do a little customization of car behavior. It's all software and it's for the sake of efficiency.
 

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Tell us more about your RAV4EV. How many miles are on your battery pack? From what I hear they last a very long time, contrary to everything GM says about NiMH batteries.
 

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I agree with you 100% that the user should have more manual control over the genset. The one-mode-for-everyone isn't going to work. I also feel that the Volt really needs ultra caps to act as a buffer between the motor and the battery, and the battery and the genset- especially for those that need on-demand power (those in mountainous areas or those that are just spirited drivers). I have a bad feeling first generation Volts without ultracaps will end up being a problem in about 5 years for those that place unusually high demand on their packs.
 

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Yeah ultracaps would be awesome. Ultracapacitors can absorb more energy through regenerative breaking than batteries, can't they? I guess that would depend on the vehicle and driving habits.

It's all about cost. New manufacturing techniques will bring down the cost of batteries and capacitors in the near future. The batteries wouldn't be such an issue if it wasn't for chevron though. :(
 

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This data provided by Doug Korthof.

Study of the internal resistance and performance of a RAV4-EV with
91,943 miles.

Internal resistance varies depending on temperature and state of
charge, so this is approximate.

The RAV4-EV gauges tell you, in a general way, what real
instrumentation shows exactly. If the RAV4-EV had not been killed
by the Chevron-funded lawsuit, we would no doubt see better
instruments.

For example, some RAV4-EV show "full" at the top bar; others can
store 10% more energy than this mark.

Internal resistance is, in general, BAD; it shows the battery has
been abused, or is just aged.

We look for an even reading of internal resistance, in Milli Ohms,
to tell the state of the pack -- its "youth", as it were.

The EV-95 might be "born" with 4 MO resistance, but is kaput when it
gets to be about 70 MO to 90 MO.

Toyota has turned over all their battery service to one company,
which has not been forthcoming with battery performance data.

This pack has a very SMALL voltage drop when acceleration is applied
or for hill climbing. This is GOOD, and tells us, in a non-
technical way, that the internal resistance has not gotten too high.

But we want to know for sure, and know exactly, to add to our
knowledge of how NiMH batteries perform as they age.

RAV4-EV-Info reports 12.6, 12.7, 12.6 which we will find to be
pretty accurate for average, max and minimum voltages.

SOC........: 35.8%
Voltage....: 303
Odometer...: 91,943
Temperature: 23 C ambient, max, min and average.

Battery...VOLT.....Internal
Module....AGE......Resistance

01........12.6......07
02........12.6......07
03........12.6......07
04........12.6......07
05........12.6......07
06........12.6......07
07........12.6......07
08........12.6......07
09........12.6......07
10........12.6......07
11........12.6......07
12........12.6......07
13........12.6......07
14........12.6......07
15........12.6......07
16........12.6......07
17........12.6......07
18........12.6......08
19........12.6......07
20........12.6......07
21........12.6......07
22........12.6......07
23........12.6......07
24........12.6......07

Diagnosis: This pack has aged well; it hasn't been "leveled" more
than once per month, but it's pretty regular in the individual cell
voltages as judged at the module level.

This pack is still pretty fresh, even at 91K miles. It has not been
over-charged or abused in any apparent way.

The one high reading, 8 MO on module 18, bears watching but isn't
entirely unusual.
 

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Discussion Starter #8
Hi Lyle. The RAV4 works very well in the cold, although on a cold snowy day, I use the heat pump, wipers, headlights, heated seats, heated windshield and the rear defroster . Add in lower tire pressure from lower temps, plus lower temps in the differential oil, wheel bearing grease, and generally thicker air (more air resistance). Make matters worse by having a road with wet snow on it, and the car must push that snow out of the way while driving. Then of course, there are the batteries which aren't as efficient at low temps. And guess what happens? It still works! Yes, the car doesn't go as far, but I only drive about 50 miles a day, so I still get home without issue. Granted, I have to use more of the SOC than I'd prefer, but the car works very, very well. The cold is very good for the batteries, it should help them last a long time. I bet the car would go about 70 miles on a charge in the worst winter conditions, and in the summer, go about 100 miles on a charge. I have about 72,000 miles on the car (original batteries) and it still works great. It's true, NiMH is awesome for longevity.

You are right about the "no regen" being the best for range. The car goes farther when you coast rather than slow down every time you lift your foot off the "go" pedal. I can turn this on and off dynamically in my car.

Mausoldj, your comment about what could be developed is indeed the ultimate goal. The issue at hand is that engineers are not magicians or mind readers, they must use the available data to develop the algorithm, and there is no way that I can think of that the car could know you are almost home (and going there), or climbing a mountain, or going on a long trip. I've thought about GPS, but that seems like more trouble than a mode switch. In the end, the algorithm must mimic the real world, and I just don't see how it could be done.

I encourage everyone to ponder my scenarios and lay out a solution. I fear this car will be built with permanent commute mode and will suck at mountain climbing and will be less than optimal for long trips.

Nate
 

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Thanks for the info Nate! I've got another question along the lines of your question.

"Let's suppose I live a the top of the mountain, and can regen all the way down to work in the morning. (Like people here in Denver do). I might need the car to charge only until halfway, then regen down the mountain until the SOC is full, ... "
In the above scenario let's assume the car if fully charged before driving down to Denver. How will the car handle regen? If the battery is fully charged, it will become overcharged. If overcharging is to be prevented, the car can't turn off regen going down a mountain, the brakes would be cooked and eaten-alive, also potentially very dangerous. ICE vehicles have engine breaking, the old downshift the transmission routine. What will the Volt do? Will a resister network be installed somewhere there is lots of outside air to dump the excess regen energy in?

How does the RAV4e handle that or does it?
 

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Hi Nate, good to hear from you again.
I think your thoughts are excellent. The only thing that comes to mind is that the selectable modes would be better suited/more needed if the ICE of the Volt was going to be smaller. But at 1.3L it should be able to supply all necessary charge to the battery under all conditions and since there is no connection b/w the ICE and the drive train I'm not sure there's much if any advantage to maintaining a particularly high SOC.

Now, if it is necessary for the ICE to run outside of it's most efficient mode in order to sustain the battery charger in either mountain or Long trip mode then your idea could, indeed, be pretty useful for optimizing FE when the ICE must run.

Any thoughts on how/when you would want to disable mountain climb mode? What I'm thinking here is that while higher SOC is desireable as you ascend, near the crest you'd want to go ahead and shut down the ICE and begin to deplete the battery so that you have room for regen and recharge as you descend the other side of the mountain or for your return trip down the mountain.
 

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Engineers could develop a Computer Algorithm to determine the mode, ensuring seamless mode switchover.
Nope the O/P is correct, the computer has no way of knowing if you are almost home or need to top off the battery because you are about to climb a long hill or mountian
 

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Discussion Starter #12
Thanks for the info Nate! I've got another question along the lines of your question.

In the above scenario let's assume the car if fully charged before driving down to Denver. How will the car handle regen? If the battery is fully charged, it will become overcharged. If overcharging is to be prevented, the car can't turn off regen going down a mountain, the brakes would be cooked and eaten-alive, also potentially very dangerous. ICE vehicles have engine breaking, the old downshift the transmission routine. What will the Volt do? Will a resister network be installed somewhere there is lots of outside air to dump the excess regen energy in?

How does the RAV4e handle that or does it?
Hi Lyle. If I lived in the mountains, I would charge to less than 100% each night before heading down in the morning. My mountain trips have always started with a charge at the bottom only, so that guarantees that I'll never go over 100 on the way down. I have heard stories about RAV4 EVs getting too full coming down a mountain and warping the rotors. They are solid aluminum through 2002, then vented steel through 2003. I don't think the situation is bad enough to cause brake fluid boiling and total failure.

A solution to this, I think, would be to engineer the max regen mode to actually spend excess power to apply torque on the electric motor in the opposite direction. My car has reverse (motor spins backward) so it seems this would be possible. Does anyone know if this is theoretically possible? I do not know.

Nate
 

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Regen Braking when SOC is high

Lyle wrote:
"let's assume the car if fully charged before driving down to Denver. How will the car handle regen?"

I have a 2000 Ford Ranger EV. It has two modes, drive and ecomony. The owners manual says to use "Drive" for highway and "Ecomony" for city. As I understand it the regen braking is more aggresive when in ecomony mode.

I have read on the Ranger EV memberslist that it is better not use the ecomony mode when SOC is greater than 80% but the owners manual doesn't say anything about that. This is so the batteries don't overheat or overcharge.

Mine is Pb-acid battery and the batteries are eight years old so I'm on borrowed time. My daily drive starts out up and down a steep hill then on flat land after that. I always use "Economy" mode but I'll try the hilly part in "Drive" mode and see how it affects my SOC and range.
 

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Simple solution, and my apologies if someone else already mentioned this, as I did only scan most of the replies...


Integrate the charging computer with a GPS. Provided the user actually uses the GPS and sticks to the prescribed route, the charging computer could then calculate the ideal charging scheme for that particular route.
 

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Simple solution, and my apologies if someone else already mentioned this, as I did only scan most of the replies...


Integrate the charging computer with a GPS. Provided the user actually uses the GPS and sticks to the prescribed route, the charging computer could then calculate the ideal charging scheme for that particular route.
Even Bob Lutz has mentioned that, so you KNOW it's not a new idea. ;) Granted, he wasn't talking about using the GPS quite in that way, he was talking about having it relax charging requirements if you're near home, but once you set it up for one, it's an easy win to include the other. You've already spent the money putting in GPS and integrating it with the power control software.
 

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Interesting. Having never driven one, I would have assumed that a manual selector switch between (at a minimum) "Low" and "High" SOC would be included in every hybrid. I'm genuinely surprised that this isn't a standard feature already, although I guess I shouldn't be.

Hopefully GM figures this out (or reads your post and pays attention) and gets it right in the Volt. :)

- Kaspre.
 
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