Prius Fun
erco
Posts: 20,260
I'm still trying to fathom·just how a Toyota Prius gets·better MPG in city driving·than highway (51 vs 48). http://www.mpgfacts.com/?did=476&year=2010··· Sure, average city speeds are lower than highway speeds, so the cumulative energy required to fight aerodynamic drag is lower in the city test. And I get that regen braking in the city converts some mech energy back into storable electricity, but never at 100% efficiency.·There are losses at every turn, both literally and figuratively. At the end of the day, gas in the tank was burned to power the ICE, which provided mech power to move the car and charge the batteries back to full. Furthering that line of thought, a small-gasoline-engined car should be able to nearly approach Prius' highway mileage. Yes·its ICE engine·would be slightly bigger·than the Prius', but·deleting·two electric motors and a huge battery and control system saves weight and those associated inefficiencies. I'm constantly having this debate with engineers and Prius owners, but I haven't been bowled over by anyone's explanations yet. I can believe that·our government's MPG-rating system has some lopsided peculiarities that·make for an apples·& oranges comparison in the case of a hybrid.·I respect the aggregate knowledge pool here in the P'lax forums, so if you have·some informed insight beyond "it just works out that way" (I hear that a lot from people who should know better), feel free to chime in here.
Enough "grumpy old engineer".·The real purpose of·this post is to share a nifty Prius web site I just found. I really like the description and user-adjustable sliders in the PSD animation at http://www.eahart.com/prius/psd/·. A great web-based model that is fun to play with. I know the "Prius effect" is how people learn to drive more efficiently just because we are all fascinated by colorful animated computer screens. Anything that remotely resembles a video game brings out·our geeky competitive side.
The links at the bottom of the page go to some very interesting sites that I haven't fully explored. Perhaps my answer lies within...
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·"If you build it, they will come."
Enough "grumpy old engineer".·The real purpose of·this post is to share a nifty Prius web site I just found. I really like the description and user-adjustable sliders in the PSD animation at http://www.eahart.com/prius/psd/·. A great web-based model that is fun to play with. I know the "Prius effect" is how people learn to drive more efficiently just because we are all fascinated by colorful animated computer screens. Anything that remotely resembles a video game brings out·our geeky competitive side.
The links at the bottom of the page go to some very interesting sites that I haven't fully explored. Perhaps my answer lies within...
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·"If you build it, they will come."
Comments
-Phil
As for the 51 city/ 48 hwy, the approx 6% difference in the two would suggest that it might be difficult for the average interested owner to duplicate the figures in any consistent or repeatable way.
Any prius owners here to set the record straight?
Cheers,
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Tom Sisk
http://www.siskconsult.com
·
I had a Chevy Nova that was built on a Toyota assembly line and the car saved more gas than today's cars because the engine was smaller and it sipped less gas than my Hyundai Elantra and it used less gas than the "fuel efficent" Honda CRV. Car companies have been making and selling cars based on more horsepower which is rediculous because you still have to follow the speed limit and you still have to stop for the same light that the guy with less horsepower has to stop for. You both get there at reasonably the same time. There were people who use to use route 80 to go from Pennsylvanis to commute to New York and when the price of gas rose, these big SUVs became lawn ornaments all over the place. I buy 87 gas because I feel that buying 89 or higher is just throwing money away.
I have some relatives who have a hybrid and they can't really tell me the savings.
There are problems with the Prius and I may not be up to date on the information:
When you are in an accident, you are locked in the car because there may be wires exposed and the car makers don't want you electricuted.
Some people decide to send their cars to the junk yard rather than sell it or give it to others because they have problems with the battery and they don't want other people to get hurt.
I think the Prius had the tires filled up with Nitrogen to create heat. This breaking makes the tires wear out faster and the tires are expensive.
What do you do when it is time to replace the battery? It is an expensive part of the car.
Chuck
Regarding the highway/city mileage difference, it is possible most of that difference is due to drag. The relationship between drag and wind speed is not a simple linear one.
· Reminds me of this·train commercial that says a train can carry 1 ton of freight 400 miles on 1 gallon of fuel.
· I call BS. Maybe (maybe) on the AVERAGE. But if I had a locomotive and put 1 ton of "freight" on it, and put 1 gallon of fuel in the tank...NO WAY is going to travel 400 miles.
· Okay, you say well if you use 100 tons of freight, and 100 gallons....But that is NOT the same thing.
· And I've listened to the train commercials, they do not say "average".
Bean
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Use BASIC on the Propeller with the speed of assembly language.
PropBASIC thread http://forums.parallax.com/showthread.php?p=867134
March 2010 Nuts and Volts article·http://www.parallax.com/Portals/0/Downloads/docs/cols/nv/prop/col/nvp5.pdf
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There are two rules in life:
· 1) Never divulge all information
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If you choose not to decide, you still have made a choice. [noparse][[/noparse]RUSH - Freewill]
On the highway, the prius is using the gas engine only. The Electrics are not strong enough to run at highway speeds, so the gas is used. In the city, the engine is shut off at lights, regen braking us used, the batteries/motors can handle the load, and the motor is only used to charge the batteries (at a constant, max. efficiency mode). This is why they are better in the city. This is contrary to many of the other hybrid or electric vehicles, which focus more on highway driving efficiency. The Prius was designed for city driving (designed in Japan, made for Tokyo driving, etc...)
This is my understanding, at least.
-Parsko
If these use less power to use them on battery power, then recharge the battery? As opposed to leaving them plugged in to AC power all the time while using them?
Say a laptop. Would a laptop use less electricity if you used it on battery for an hour, then after that, recharged the battery until it was fully charged?
Would it use more electricity to leave it plugged into an outlet for the hour you were using it?
And if you use a laptop battery for an hour, does it take an hour to recharge it? Or more/less time?
With some rechargeable battery powered things I have,·I seem to be able to use them for quite awhile, but they recharge·very quickly.
Also you could convert this to recharging with a portable electric generator in the above test. If I was using a cordless drill for an hour off and on and also had this plugged into a generator which was running for that full hour, I would use an hours worth of gas in the generator. However I might be able to use·the drill·on battery for an hour, then start up the generator and recharge that battery in 5 minutes, then use only 5 minutes worth of gas to power the generator!
Note: Something else interesting about electric powered vehicles is that the fastest charger for one electric vehicle uses 70 amps of 240 volt AC electricity and will recharge in 4 hours...
...many homes have a 200 amp electric service...
...let's see... Summer: air conditioning going full blast, kitchen range going, washer/dryer going, dishwasher going, would there be 70 amps spare to recharge that vehicle?...
...then husband's car 70 amps, wife's car 70 amps, son's car 70 amps, and daughter's car 70 amps... Add that up!
...and say they had upgraded to a 400 amp electric service. And so did their neighbor. And everyone else... Then you get·into peak electric use times where there is currently not enough electricity to power everything... Hummmm...
And California had a fit about these new TV's using a bit more wattage and the combined new electric usage stressing the electric grid to the max. Wait till everyone gets electric vehicles!
The power consumed by a vehicle in overcoming aerodynamic resistance is proportional to the cube of the velocity. All other power losses [noparse][[/noparse] rolling friction, mechanical losses] are somewhat linearly proportional to velocity. So if you are cruising at steady, low-speed, driving in the city you get better mileage. But, in the city there is much acceleration/deceleration. And a gas engine is not nearly as efficient under an acceleration load as under a relatively constant load [noparse][[/noparse]ie. cruising or charging batteries]. You can see this in a regular modern car which displays instantaneous MPG wherein while accelerating the mileage goes way down. Therefore if you can use the gas engine to charge batteries and use the battery power to run an electric motor to do the accelerating [noparse][[/noparse]at much greater efficiency] you should get better mileage in the city where the steady-state power needs are less.
Also, a significent amount of energy is lost thru heat in braking, which, of course, takes place more in city driving. In a gas car this is totally wasted. The Prius takes advantage of this energy by turning the electric motors into generators; which also recharge the batteries.
[noparse][[/noparse]A 3000 hp diesel/electric locomotive does almost all of it's braking in the 'Prius' manner but wastes it through forced air-cooled resistors on the roof. Picture a train of loaded coal cars on a downgrade and calculate how much heat is in 3000 hp!]
Enough.
cheers, David
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Lots of propeller based products in stock at affordable prices.
More food for thought: the Prius gas engine·uses a modified combustion cycle, the Atkinson cycle, which achieves higher efficiency due to a linkage which yields a power stroke that is longer than the compression stroke·(different strokes for different folks): http://en.wikipedia.org/wiki/Atkinson_cycle
And·even mo'·info from Wiki: ·http://en.wikipedia.org/wiki/Toyota_Prius
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·"If you build it, they will come."
-Phil
Post Edited (Phil Pilgrim (PhiPi)) : 5/17/2010 5:19:13 PM GMT
Sorry, but I don't really agree with that. There is nothing wrong with cars that have decent power get good mileage. Detroit has recently been making some cars that are both fun and economical. Just look at the new 2011 Mustang which has good power and economy as one example. With the fuel management most engines will only use as much fuel as requested by the pedal. Use it lightly and you'll see the results at the pump. Just because a motor can make more power that doesn't mean that it uses extra fuel if drive it as if it didn't.
From my own experience a huge factor in the mileage has to do with driving habits. Some of the HP is there if you need it but if you drive them easy you can get good mileage. Perhaps some people can't control themselves and mileage suffers as a result. I'd rather have a little extra power on demand (if needed) then not have it available. A couple years ago when my car was flattened by a neighbors tree I had to look at new cars. I wanted something economical and ended up getting a 2008 Chevrolet HHR SS. It gets excellent mileage, good utility, fantastic handling, and is quite fun to drive. It is very practical. Although it can put out close to 300HP the 2.0L engine can also sip gas. It is actually smaller than the 2.2 and 2.4L engines w/less HP. I've gotten over 35mpg on recent trips with careful driving on mine.
Robert
Post Edited (RobotWorkshop) : 5/17/2010 5:57:56 PM GMT
Very misleading since they are counting the energy stored in the batteries, which comes from the power grid, in their calculation. It's like stating the mpg of a sailboat.
Rich H
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The Simple Servo Tester, a kit from Gadget Gangster.
Does it matter if you can use a single gallon to move a train? Trains operate on a huge scale, just like cargo ships and the rest of our economy. Where I live, a dozen trains 100 cars long with 200 containers pass every day. It doesn't matter to the shipper that they move the freight hundreds of tons at a time, all that matters is that they get their stuff from A to B. The railroads figure out how much diesel they use on the journey and the freight moved, then they have their number. The train rating can't be compared to a car since the car is the base case and economies of scale don't affect the rating.
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Powered by enthusiasm
as for milage vs engine size. the smaller the engine the less space for the combustion. This means less energy is required to move the pistons, so smaller does mean less energy. though the cars mass, erodynamic footprint, and driver have more to do with economy then anything.
My 2006 pontiac vibe(made by Toyota in partnership with GM) is raded at 6.5L/100km. If I try I can get the fuel economy down as low as 5.5L/100km(savings of $6 to go see my inlaws and $50 to see my parents) just by obeying the speed limit, allowing the car to accelerate and decelerate over hills, and taking advantage of other cars to break the wind(don't drive to close even 10 car lengths back from a transport will save you gas and is safe to drive. you need to be able to see there mirrors.)
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Lots of propeller based products in stock at affordable prices.
Must be·a petroleum industry conspiracy. All those 200 MPG carburetor guys disappeared long ago...
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·"If you build it, they will come."
YES IT DOES MATTER.
If my pickup can move 1 ton of freight at 60 MPH, would it be correct to say that it can move 1 pound of freight at 120,000 MPH ?
Bean
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Use BASIC on the Propeller with the speed of assembly language.
PropBASIC thread http://forums.parallax.com/showthread.php?p=867134
March 2010 Nuts and Volts article·http://www.parallax.com/Portals/0/Downloads/docs/cols/nv/prop/col/nvp5.pdf
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There are two rules in life:
· 1) Never divulge all information
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If you choose not to decide, you still have made a choice. [noparse][[/noparse]RUSH - Freewill]
http://www.ecrostech.com/prius/original/Understanding/InternalCombustion.htm
The author goes into some interesting detail:
I mentioned above that the Prius engine is based on the same configuration and cylinder dimensions as the Echo engine. ·It should be clear after this discussion of the Atkinson cycle that this similarity is misleading. ·Under most conditions, the Prius will give better fuel economy than the Echo, even though the engine is pulling a larger and heavier car. ·The improvements in economy are not only due to the hybrid system but also due to engine design. ·Even when the ICE is running all the time, as in freeway driving, the Prius can give greater economy than the Echo.
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·"If you build it, they will come."
Bean;
Are you just picking apart the way the add was worded, or questioning the validity of rail transportation?
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John R.
Click here to see my Nomad Build Log
During hard acceleration the electric motor will draw from the battery to assist the engine.
For those of you that haven't driven(or owned) a prius the first thing you have to get use to is an extremely sensitive gas pedal.
There are tricks you can do to get better mileage but you have to drive it a few weeks to get a feel for it.
In our case I figured out that if the heat/ac,lights,radio,etc are all turned off I can drive 38mph for about 1.3mi on battery power. Everyone I've talked to says this is impossible, but some how I've been able to pull it off the last three times I drove it.
The nitrogen in the tires is because of the aluminum wheels and cheap tires. Nitrogen has larger molecules than air and thus is less likely to leak out through the porous aluminum and rubber.
-dan
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(Former) Caterpillar product support technician
If the ad had said "on average" I would agree, but it doesn't.
Bean
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Use BASIC on the Propeller with the speed of assembly language.
PropBASIC thread http://forums.parallax.com/showthread.php?p=867134
March 2010 Nuts and Volts article·http://www.parallax.com/Portals/0/Downloads/docs/cols/nv/prop/col/nvp5.pdf
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There are two rules in life:
· 1) Never divulge all information
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If you choose not to decide, you still have made a choice. [noparse][[/noparse]RUSH - Freewill]
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John R.
Click here to see my Nomad Build Log
A few years back one of my neighbors sons traded in the car he inherited from his parents for a high powered sports car. The morning after he got it he jumped in the car, started it up, and stepped on the gas to back out of the driveway. The car crossed the road, went over the lawns and gardens of two houses across the street from his house, crossed back over the road, went across another lawn, knocked down a tree, and ended up on the porch of the house. Luckily there were no kids out playing that early.
While I agree that having a car with good handling and adequate power for passing is great, there is such a thing as too much. A car with a 300 horsepower engine may be fine for an experienced driver, but it is probably far more than a new driver on a testosterone high can handle.
The primary reason for using nitrogen in aircraft tires is to prevent corrosion. Compressed air is mostly nitrogen (~80%), but the oxygen (~20%) and water make a corrosion friendly atmosphere.
Never heard the thing about air leaking out through the aluminum.
Rich H
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The Simple Servo Tester, a kit from Gadget Gangster.
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Lots of propeller based products in stock at affordable prices.
@mctrivia, I doubt very much that nitrogen in the tires makes any difference in the great white north. After sitting in sub-zero temperatures over night the rubber will be relatively inflexible and have a higher rolling resistance regardless of the gas inside. The flat area in contact with the ground could even cause a slight "thumping" until the tire warms up. I have noticed that effect a few times when visiting Thompson Manitoba in winter.
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·"If you build it, they will come."
I wonder why they think nitrogen would help with that?
I think this is like those multi-thousand dollar power cables. Those that fall for the hype and spend the money on it will perceive a benefit. Word got around that high performance aircraft used nitrogen in their tires so the consumer wants it too. Those that sell it will provide reasons why you are a fool not to use it.
There's no reason not to use it if you want to, if I had some here I'd probably put it in my tires. As it is I only have O2 and N2O. Either would probably be really bad in a tire so it's it just regular ole compressed air for me.
Rich H
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The Simple Servo Tester, a kit from Gadget Gangster.
Basically the consensus that I get is if you are going to have a large temperature change(like on a plain) then Nitrogen is much better but BS if on a car.
I do know that at -50C last winter my tires got nice and square(well flat on bottom round the rest of the way) which made some nice thumping sound until the tires warmed up from driving. At the crazy cold temperatures we can get way up here it may make a difference. can't say since I don't have nitrogen in my tires.
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Lots of propeller based products in stock at affordable prices.