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What is the maximun hill grade limit that the Prius can handle and for how long can it go while going up it. I read on a website that if the battery runs out on the way up a hill, the ICE will have to do all of the work and not be able to handle it for very long. Any comments???
 

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Brian said:
What is the maximun hill grade limit that the Prius can handle and for how long can it go while going up it. I read on a website that if the battery runs out on the way up a hill, the ICE will have to do all of the work and not be able to handle it for very long. Any comments???
I have but one comment and that is, You are very funny.

Moo :)
 

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i wasn't trying to be funny, but when i read about the battery it kinda scared me because i live in an area where there are alot of hills. But glad to give some laughs.
 

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I've seen photos posted of both Classic and '04 Prii parked at the top of Pike's Peak. Many people have relayed stories of their trips over Vail Pass in Colorado with their Prii. No one has, to my knowledge, complained of any difficulty what so ever with those trips and most relate that they seem to do well passing other vehicles.

So, unless you intend to try to climb grades longer and/or steeper than that to Pike's Peak I think the Prius will hold it's own.
 

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Brian said:
i wasn't trying to be funny, but when i read about the battery it kinda scared me because i live in an area where there are alot of hills. But glad to give some laughs.
Brian,
Sorry for my quip. I thought you were joking. The straight answer to your question is, No, the Prius will not lose power driving up a long, steep hill. The Prius is not an electric car, it is a gas-electric hybrid, which recharges it's batteries continuously--even, if necessary, while driving up hill. Snoop around here for a while and you will learn lots of useful information about this amazing technology. FWIW, I live in a hilly area as well and I drive my '04 Prius into the mountains each weekend (elevation gain of approximately 4000 ft.) with no difficulty whatsoever. If not for the unusual screen mounted in the middle of the dashboard, most passengers would never suspect they were riding in anything other than a normal gas-powered vehicle.
Drive happy,
Moo :)
 

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When I took my '01 up Mt. Washington in NH, I was able to drain the battery to the point that it would not assist. The gas engine still had sufficient power that I was only limited by my driving ability, not the engine power (mostly 35 MPH with bursts to 40+). The only noticeable effect was a second or so lag between requesting and getting power.

I have read accounts of an interstate climb in Colorado (maybe called Eisenhower tunnel?) that drains the battery to the point that you are forced to slow down to 60-65 MPH for a short while before reaching the peak. Note that even at this slower speed, the writers claimed to be passing many vehicles having a much worse time of it.

There have been reports of an isolated (dirt?) road near San Francisco that the '01-'03 cannot climb in reverse, though it can climb it forward.

I suspect that the '04 with it's higher power battery and engine doesn't have any of these limits.

Even with the '01-'03 these are not particular hardships, so this is a non-issue.

The other thing you may have heard is that with the manual shift version of the Honda Insight, it's possible, through bad gear selection, to run the battery down on long climbs to the point where the limits seem somewhat severe. Once the driver learns proper gear selection, the "problem" goes away.
 

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The oldest living thing on the planet are bristlecone pines. There are groves of them above 10,000 ft. in Claifornia. Certain individual trees were growing there during the time of Christ. Many of their roots are exposed as the mountains are wearing down from around them they are so old. One of the groves is a tad over 11,000 ft. Some of the roads to reach these wonderous trees are steep, quite steep. Interstates frequently don't exceed a 6% grade without a special slow truck lane. Some of these roads, if I recall correctly, are either 25 or 35% grades!

I couldn't take the pickup camper(normally asperated diesel)that I had at that time to the 11,000 ft grove as at full throttle it got slower and slower and wouln't go any more. My turbo diesel Cummins/Dodge FLEW up the same road.

If we have any Prius owners who would be interested in visiting the oldest living things on the planet we could get high altitude AND steep grade at high altitude performance reports.

Earth's oldest living inhabitant "Methuselah" at 4,767 years, has lived more than a millennium longer than any other tree. It is in the White-Inyo mountain range of California in the Great Basin National Park.

http://gorp.away.com/gorp/resource/us_n ... pin_gb.htm

In my experience there are a limited number of long long steep grades. Many mountainous roads are too twisty to drive really fast safely so the ICE alone should do fine in most cases but with some up and down grades as are frequently experienced, regenerative braking from the down hill portions should provide some energy to recycle to climb again.


:D Pat :D
 

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patrickg said:
The oldest living thing on the planet are bristlecone pines. There are groves of them above 10,000 ft. in Claifornia. Certain individual trees were growing there during the time of Christ. Many of their roots are exposed as the mountains are wearing down from around them they are so old. One of the groves is a tad over 11,000 ft. Some of the roads to reach these wonderous trees are steep, quite steep. Interstates frequently don't exceed a 6% grade without a special slow truck lane. Some of these roads, if I recall correctly, are either 25 or 35% grades!

I couldn't take the pickup camper(normally asperated diesel)that I had at that time to the 11,000 ft grove as at full throttle it got slower and slower and wouln't go any more. My turbo diesel Cummins/Dodge FLEW up the same road.

If we have any Prius owners who would be interested in visiting the oldest living things on the planet we could get high altitude AND steep grade at high altitude performance reports.

Earth's oldest living inhabitant "Methuselah" at 4,767 years, has lived more than a millennium longer than any other tree. It is in the White-Inyo mountain range of California in the Great Basin National Park.

http://gorp.away.com/gorp/resource/us_n ... pin_gb.htm

In my experience there are a limited number of long long steep grades. Many mountainous roads are too twisty to drive really fast safely so the ICE alone should do fine in most cases but with some up and down grades as are frequently experienced, regenerative braking from the down hill portions should provide some energy to recycle to climb again.


:D Pat :D

I don't know if a Prius can meet this difficult challenge or not, but here are a couple of links to other old things.

http://www.death-valley.us/article652.html

http://news.bbc.co.uk/1/hi/sci/tech/978774.stm

Live long and prosper,
Moo :)
 

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Moo, Thanks for the links. Very interesting, I wonder how many OLDEST claims there are anyway???? I guess Bristle Cone Pines are ONLY the oldest trees alive on the planet. I really like creosote bushes and they are one of the dependable desert flowering bushes in our landscape on our property down in Baja. I was not aware of their unusual daughter plant self cloning thing.

I would certainly be interested in hearing a driver report on Prius performance at high altitudes, especially above 10,000 feet. It would be interesting to see how the little high tech mill could handle the challenge. It might surprise us and do as well or better than "conventional" normally aspirated engines. I don't think it could compete with any waste gated turbo but I would like to know how it woud fare.

I can assure you that I could have used a personal turbo while hiking up there. FAA requires the pilot in command to be on oxygen or have cabin pressure for flights above 10,000 feet. When I hiked at 11,000 plus I could definitely tell the air was thinner.

Again, thanks for the neat links.

:D Pat :D
 

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:D Brian, your question is not funny, it's an excellent one, although the point is not "for how long can it go while going up", but only "What is the maximum hill grade limit that the Prius can handle?".

Yes, there IS some hill grade limit for a Prius, but it's not because of a limited battery capacity, it's because of a torque limit which is a consequence of the very specific drivetrain of the Prius.

Unlike in other cars, there is only ONE fixed reduction ratio between the driveshaft and the wheels, which is 4.113 for the 2004 Prius and 3.905 for the "classic". In other words, the Prius is always in "top gear" (it's VERY different from conventional CVTs). With conventional transmissions, in first gear the torque at the wheels shaft is much larger than in top gear, because the reduction ratio is huge, and that's the reason why it's rather easy to make the tyres slip even on a dry road when you accelerate from a dead stop (and even if you don't own a Ferrari ;) ). A gearbox is necessary in conventional cars because any thermal engine has a limited operating range (idle rpm / max rpm), and there's no electric motor to move the car. With the Prius, even though the combined hybrid system torque at the driveshaft is huge (478 Nm for the 2004 between 0 and 22 km/h), it is less at the wheels shaft than with common cars in first gear.

Now just do the maths : 478 * 4.113 = 1966 Nm at the wheel axis; the wheel radius is 0.310 m for both the european (195/55 16) and US (185/65 15) versions (see for instance http://www.tyresave.co.uk/tyresize.html ), which means a traction force T of 1966 / 0.310 = 6342 N.
Now if the mass of car is M, its weight is Mg where g = 9.8 m/s, and if the slope of the hill is X%, the projection of the weight along the ground is P = Mg*X. Therefore the limit value for X is the one for which T equals P : T = Mg*X or

X = T/(Mg)

If M = 1400kg (car+driver+some fuel), T/Mg = 6342 / ( 1400*9.8 ) = 0.462, or a 46% grade !

Of course if you add some passengers and luggage (let's say 400kg more), it can be as "low" as a 36% grade limit... but still a comfortable one, I think. 8)

Note : this calculation is valid if you're moving forward. When using reverse, the car moves only with the electric motor, which has a maximum torque of 400 Nm. The limits are therefore lower in the 400/478 proportion.
 

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frenchie said:
X = T/(Mg)

If M = 1400kg (car+driver+some fuel), T/Mg = 6342 / ( 1400*9.8 ) = 0.462, or a 46% grade!
See, Brian, I told you amazing things could be learned about the Prius around here. Frenchie is one of the best sources of Prius info on the planet. I've grown so found of him/her that I've even given my external hard drive the same name--and that's no joke! Without doing any math, I can tell you that my '04, loaded with skis and gear, a full tank of gas and two average-sized adults zips right up a 45 mile route to the ski slopes, including the last four miles which are quite steep.
Drive happy,
Moo :)
 

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Hey, how about that, hill climbing! Even the steep high altiitude hill I recalled as being posted as steep as 35% would be handled by a Prius at sea level. Now Frenchie, what is your approximation of Prius performance at 11,000 feet? Sometimes steep roads are at high altitudes.

:D Pat :wink:
 

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Discussion Starter #13
Ok, Well that gave me more than enough to answer my question.
Thanks Everyone
Brian
 

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Frenchie is one of the best sources of Prius info on the planet.
Thanks a lot Moo, but I'm a secondary one only. For a primary one see :

http://home.earthlink.net/~graham1/

Pat, I was assuming the performance was not depending on the elevation. In real world however, the engine will be less powerful at high altitudes because of lower air pressure; but the electric motor will not be affected, since it does not need oxygen... As most of the torque comes from the electric motor, there will be little difference in the hill grade limit I was talking about. But this limit is only a "static" limit (above which the car will simply not be able to move forward !) and which will probably be lowered by tyre/ground friction coefficient : I assumed also perfect adhesion !

Now if you consider several miles on steep roads, then altitude will affect performance because, the engine being less powerful, you will need more electric power, and this will discharge the HV battery more quickly. Furthermore, the engine will take more time to recharge it, since it is less powerful...

The worst case you can face is when the HV battery doesn't want to discharge anymore : you are left with the engine only, which is less powerful because of elevation. How much can the difference be ? A crude estimate can be made using an exponential law for the air pressure :

p = p0 exp [-Mgz/RT]

where p is the pressure at elevation z in meters, p0 the pressure at sea level, M the equivalent molar mass of the air (29 grams/mole), g = 9.8 m/s the acceleration at the Earth surface, R the ideal gas constant (8.31 Joule per Kelvin and per mole) and T the absolute temperature (let's take 280 Kelvins, or about 44F or 7C). The calculation gives that for 11000 feet (3353 m) the pressure is lower by a factor :

exp [(-0.029*9.8*3353)/(8.31*280)] = 0.66

At 11000 feet you get only 66% of the air pressure you would get at sea level, and therefore it is like if the engine had only 66% of its cubic centimeters. For a 1.5 l engine, that makes a 1.0 l engine... :(

But hey, this is only if you maintained maximum acceleration for a good while, and drove like nobody is supposed to drive on these splendid mountain roads... you'd better cool down and look at the scenery ! :wink:
 

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Right on Frenchie! I agree with the math but man oh man it sure felt like I lost more than 1/3 of my personal HP when I was hiking up there. I could sure have used my own personal turbo charger but my intake manifold probably couldn't take the boost pressure I would have needed to recoup the lost power due to lack of O2.

Given your earlier estimates of power to the ground assuming perfect traction, I don't think you'd be in danger of much wheel spin on dry pavement. Of course the over inflation of the tires due to the increased "gauge" pressure would lower the area of the contact patch where the rubber meets the road.

:D Pat :D
 

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Discussion Starter #16
Somebody got an A in Phyisics. That all answers my question very much with a very detailed answer. Thanks Again!
 

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I agree with the math but man oh man it sure felt like I lost more than 1/3 of my personal HP when I was hiking up there.
In my crude calculation you lose 1/3 of the engine power, but if the battery has already given all its juice there is zero electric power; compared to the normal situation where you can get both maximum engine power (57 kW) and battery power it makes more than a 1/3 decrease. Assuming 21 kW power for the battery (Toyota figure), the relative decrease is :

[(57+21) - (57*0.66)] / (57+21) = 0.52 or a 52% decrease.

Is that more consistent with your feelings, Pat ?

But again, this has to be considered as a VERY EXTREME situation, not the one you encounter in everyday driving... the Prius will behave like any other car if you don't require maximum power all the time.
 

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Frenchie, That was sort of one sided of me to only consider boosting my personal HP via a turbo, I neglected to consider electric assist. A properly applied good commercial grade cattle prod might have unleashed considerable additional HP or at least motivation and technologically enhanced enthusiasm.

Most modern cars fare so much better at altitude with their automatic computer adjusted fuel air ratio than the old fixed (manually adjusted) models of previous decades that we forget (or are blissfully unaware of) how it used to be.

Sustained hill climbing in reverse could pose a problem but only in the most extremely rare of situations where that would be required for an extended period/distance. That however, does remind me of the oddity of hill climbing in an old Ford with cowl mounted fuel tank. If you came to a hill that was so steep that the car lost power due to fuel starvation, you turned around and backed over it as the fuel pickup with a low level in the tank was better at high angles when backing.

:wink: Pat :wink:
 

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Frenchie, How true, how true! I feel there are few qualified by education and experience to do a better job of it that you or I and together, on a good day, we make a whole wit.

:D Pat :D
 
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