[Jim Thompson]

On Jul 31, 7:21 am, Jim Thompson <To-Email-Use-The-Envelope-I...@My-
Web-Site.com> wrote: [snip]

I don't ever recall saying "more-efficient-at-higher-speed".

But I guess it WOULD depend on your definition. The engine is
optimized right around 3000RPM (85MPH), but external drag is higher.

If you shift to a lower gear, 3000 RPM is at a lower speed. If there
isn't an issue that is well modeled by a fuel leak, the milage would
improve.

Ever consider that transmissions aren't equally efficient in all
gears and perhaps the over-drive locked-up may be a tad more
efficient than the lower gears? There is also work done just
spinning the engine. Me thinks you're wrong.

Don't both Honda and Toyota have models with CVT (continuously
variable transmission) which keeps engine RPM's in a narrow/optimum
range?

...Jim Thompson

 

[Jim Thompson]

On Wed, 01 Aug 2007 00:45:24 -0500, Spehro Pefhany
[snip]

I suspect Spandex is better than nothing. More slippery than hairy
surfaces and it could prevent the energy-sapping oscillation of fatty
and/or dangly bits.

Well, I suppose some people are more viscous than others.

Certainly more vicious ;-)

We have a friend who bought a Toyota hybrid. But hauling all those
batteries up and down the hills here apparently isn't efficient... her
mileage is mediocre.



People don't buy Prius' to save gas, they buy them to be hip and
stylish. So instead of smog, we have clouds of smug.

John

Bwahahahahahaha!

...Jim Thompson

 

[Jim Thompson]

Not in this graph:

http://www.fueleconomy.gov/feg/driveHabits.shtml

I've seen a few other mpg-vs-speed curves, and they all look similar.
Looks like aerodynamic drag starts to seriously kick in above 55 MPH.

John

You need to look at engine horsepower and torque versus RPM as well.

Drag DOES depend on body shape.

...Jim Thompson

 

[John Larkin]

On Jul 31, 7:21 am, Jim Thompson <To-Email-Use-The-Envelope-I...@My-
Web-Site.com> wrote: [snip]

I don't ever recall saying "more-efficient-at-higher-speed".

But I guess it WOULD depend on your definition. The engine is
optimized right around 3000RPM (85MPH), but external drag is higher.


If you shift to a lower gear, 3000 RPM is at a lower speed. If there
isn't an issue that is well modeled by a fuel leak, the milage would
improve.

Ever consider that transmissions aren't equally efficient in all
gears and perhaps the over-drive locked-up may be a tad more
efficient than the lower gears? There is also work done just
spinning the engine. Me thinks you're wrong.

Don't both Honda and Toyota have models with CVT (continuously
variable transmission) which keeps engine RPM's in a narrow/optimum
range?

...Jim Thompson

CVTs are still the holy grail of car design, but none of them seem to
work at serious horespowers. They are the equivalent of a switching
regulator.

John

 

[Spehro Pefhany]

You need to look at engine horsepower and torque versus RPM as well.

Drag DOES depend on body shape.

...Jim Thompson

For a given shape, at automotive speeds, I think there is a square law
relationship between air speed and drag.

Best regards,
Spehro Pefhany

 

[John Larkin]

You need to look at engine horsepower and torque versus RPM as well.

Don't tell me what I need to do.

Drag DOES depend on body shape.

Aero drag goes up roughly with the square of speed for most shapes.
The question is where the v^2 thing starts to dominate. The answer,
for most cars, seems to be upwards of 55 MPH. Below that, other things
seem to matter.

John

 

[Richard Henry]

You need to look at engine horsepower and torque versus RPM as well.

Drag DOES depend on body shape.

If you look at new cars offered for sle today, the shapes are all
pretty much the same, especially when compared to the wide variations
on the market 40-50 years ago. I imagine that is because everybody's
wind tunnels give the same answers.

 

[Eeyore]

Both hybrids would get far better mileage if the batteries, the
electrics, and all the fancy controls were dumped. What's left would
be a small, light, slippery, ugly car with a small engine. All you'd
give up is acceleration and the questionable advantage of regenerative
braking, a small price to pay for dumping the batteries.

In city driving it's regenerative braking that can make a huge difference. The
complexity of shoving electrical and ICE motive power through some combined
transmission seems plain daft though. The series hybrid (in which the ICE simply
recharges a battery) seems far more sensible all round.

Graham

 

[Eeyore]

E.g. a mediocre Golf diesel will hold as much people/ luggage as a
Prius, has comparable mileage, is better made, way cheaper. It's a
mid-sized family car. There are more like those.

The official US figures don't agree with you.
http://www.fueleconomy.gov/feg/noframes/20801.shtml

Graham

 

[Joerg]

On Jul 31, 7:21 am, Jim Thompson <To-Email-Use-The-Envelope-I...@My-
Web-Site.com> wrote:
[snip]

I don't ever recall saying "more-efficient-at-higher-speed".

But I guess it WOULD depend on your definition. The engine is
optimized right around 3000RPM (85MPH), but external drag is higher.


If you shift to a lower gear, 3000 RPM is at a lower speed. If there
isn't an issue that is well modeled by a fuel leak, the milage would
improve.

Ever consider that transmissions aren't equally efficient in all
gears and perhaps the over-drive locked-up may be a tad more
efficient than the lower gears? There is also work done just
spinning the engine. Me thinks you're wrong.

Don't both Honda and Toyota have models with CVT (continuously
variable transmission) which keeps engine RPM's in a narrow/optimum
range?

...Jim Thompson

CVTs are still the holy grail of car design, but none of them seem to
work at serious horespowers. They are the equivalent of a switching
regulator.

It is, in a way, done with switching regulators. A small engine runs at
a fairly constant rpm and drives a generator. That goes into a switcher
which in turn feeds one or more motors that drive the car. The balance
goes into a battery and the engine stops when that's topped off. Pretty
much the hybrid concept.

AFAIR the closest recent approach to a roadworthy CVT was from Ford but
I haven't heard about it in a long time. The first mainstream CVT in a
car was actually brought to market in the 50's. My mom had a "DAF 44", a
Dutch car. A picture is worth a thousand words, so this is a picture of
the CVT in that type of car:

http://upload.wikimedia.org/wikipedia/commons/3/3d/DAF_Hinterachsantrieb.jpg

I became intimitely familiar with this CVT because as a kid I had the
"pleasure" to take the whole heavy CVT out. Only to find out that all
that was broken was a small governor weight in one of the "bells". Could
have fixed in with the CVT in the car. Arrrgh.

This car only had a "forward-reverse" switch and no clutch, plus another
smaller switch to increase rpm while muffling the throttle. The only
passenger car I ever saw that had a kind of jake brake. The car could go
80mph in reverse and in the Netherlands they actually had "reverse
races". Naturally, DAF was the only brand of car that could play. I
tried it once but quickly gave up because you can easily roll the car
that way.

Quite innovative but because of the belt friction the fuel consumption
was rather dismal, couldn't yield much better than 25-30mpg and that was
not good enough for European standards. IIRC the company sold out to
Volvo and then this concept petered out.

 

[Eeyore]

For a given shape, at automotive speeds, I think there is a square law
relationship between air speed and drag.

You are correct at higher speeds. The relationship isn't simple it seems.
http://en.wikipedia.org/wiki/Drag_(physics)

Drag coefficient can make collosal differences too.
http://en.wikipedia.org/wiki/Drag_coefficient

Unfortunately current US styling (the trend for truck like 'slab fronts' ) is producing
cars with greater rather than lesser drag.

The current hybrids also use skinny tyres to reduce rolling resistance. I hate to think
of the adverse effect on road holding.

Graham

 

[Vladimir Vassilevsky]

MooseFET wrote:

The power companies can't be counted on to build up the grid.
Spending on new stuff would cut into this months profits. If it
doesn't look like the grid will support it, people won't buy the
cars. When people don't buy the cars no new grid is needed.

BTW, at the beginning of the 20th century, one could buy gasoline only
in the drugstores...


Vladimir Vassilevsky

DSP and Mixed Signal Design Consultant

http://www.abvolt.com

 

[Eeyore]

If you look at new cars offered for sle today, the shapes are all
pretty much the same, especially when compared to the wide variations
on the market 40-50 years ago. I imagine that is because everybody's
wind tunnels give the same answers.

Tatra (Czech) apparently knew the answer over 70 years ago.
http://en.wikipedia.org/wiki/Tatra_T77
Cd said to be 0.212

Cd alone is only half the answer. Frontal area is equally important so the US trend for
large high-riding vehicles with a poor shape for drag loses on all points.

Automobile examples of CdA ft² are shown below:

CdA ft² Automobile model

3.95 1996 GM EV1
5.10 1999 Honda Insight
5.71 1990 Honda CR-X Si
5.76 1968 Toyota 2000GT
5.80 1986 Toyota MR2
5.81 1989 Mitsubishi Eclipse GSX
5.88 1990 Nissan 240SX
5.92 1994 Porsche 911 Speedster
5.95 1990 Mazda RX7
6.00 1970 Lamborghini Miura
6.13 1993 Acura NSX
6.17 1995 Lamborghini Diablo
6.27 1986 Porsche 911 Carrera
6.27 1992 Chevrolet Corvette
6.35 1999 Lotus Elise
6.40 1990 Lotus Esprit
6.54 1991 Saturn Sports Coupe
6.57 1985 Chevrolet Corvette
6.77 1995 BMW M3
6.79 1993 Toyota Corolla DX
6.81 1991 Subaru Legacy
6.90 1993 Saturn Wagon
6.93 1982 Delorean DMC-12
6.96 1988 Porsche 944 S
6.96 1995 Chevrolet Lumina LS
7.02 1992 BMW 325I
7.04 1991 Honda Civic EX
7.10 1995 Saab 900
7.14 1995 Subaru Legacy L
7.34 2001 Honda Civic
7.39 1994 Honda Accord EX
7.48 1993 Chevrolet Camaro Z28
7.57 1992 Toyota Camry
7.69 1994 Chrysler LHS
7.72 1993 Subaru Impreza
8.70 1990 Volvo 740 Turbo
8.70 1992 Ford Crown Victoria
8.71 1991 Buick LeSabre Limited
9.54 1992 Chevrolet Caprice Wagon
10.7 1992 Chevrolet Blazer
11.6 2005 Ford Escape Hybrid
11.7 1993 Jeep Grand Cherokee
16.8 2006 Hummer H3
17.4 1995 Land Rover Discovery
26.5 2003 Hummer H2

Graham

 

[René]

The official US figures don't agree with you.
http://www.fueleconomy.gov/feg/noframes/20801.shtml

Graham

OK you win
not sure what are the export models shown here.
I was led to believe that smaller engined models could make it.


(not even counting the energy in making the car!)

Anyway, the "3 liter Lopo" (smaller brother of the Golf, designed for
economy - 4 person 5 door car) does 70 mpg.

(And, incidentally, I like a V8 Mustang a lot better

 

[Spehro Pefhany]

The official US figures don't agree with you.
http://www.fueleconomy.gov/feg/noframes/20801.shtml

Graham

Quite a difference there.

Golf diesel is 28/39 mpg for the automatic vs. 48/44 mpg for the
Prius (2008 method, US gallons). 70% more miles per gallon in the
city.

BTW, the Golf is considered a "compact" car, not "mid-size". The
Beetle is sub-compact. I doubt a Golf will easily accept, say, a
hockey bag, stick and several people. VW "better made" than Toyota?
Not in my experience. The parts are just as expensive as Japanese, but
the reliability is more like US.

Best regards,
Spehro Pefhany

 

[Jim Thompson]

On Wed, 01 Aug 2007 08:26:13 -0700, Jim Thompson
[snip]

You need to look at engine horsepower and torque versus RPM as well.

Don't tell me what I need to do.

Eh? Didn't get any last night, John? You sure are cranky ;-)

Aero drag goes up roughly with the square of speed for most shapes.
The question is where the v^2 thing starts to dominate. The answer,
for most cars, seems to be upwards of 55 MPH. Below that, other things
seem to matter.

John

I think, if you will follow my advice, see the horsepower peak in that
region as well.

...Jim Thompson

 

[Spehro Pefhany]

On Wed, 01 Aug 2007 08:26:13 -0700, Jim Thompson
[snip]

You need to look at engine horsepower and torque versus RPM as well.

Don't tell me what I need to do.

Eh? Didn't get any last night, John? You sure are cranky ;-)

Aero drag goes up roughly with the square of speed for most shapes.
The question is where the v^2 thing starts to dominate. The answer,
for most cars, seems to be upwards of 55 MPH. Below that, other things
seem to matter.

John

I think, if you will follow my advice, see the horsepower peak in that
region as well.

...Jim Thompson

I wonder at what speed a 500HP 'vette is most efficient? ;-)

Best regards,
Spehro Pefhany

 

[Eeyore]

OK you win
not sure what are the export models shown here.
I was led to believe that smaller engined models could make it.

(not even counting the energy in making the car!)

Anyway, the "3 liter Lopo" (smaller brother of the Golf, designed for
economy - 4 person 5 door car) does 70 mpg.

I think you mean the 3 CYLINDER Lupo. It has a 1.2 litre turbodiesel engine.
http://en.wikipedia.org/wiki/Volkswagen_Lupo

Graham

 

[Spehro Pefhany]

I think you mean the 3 CYLINDER Lupo. It has a 1.2 litre turbodiesel engine.
http://en.wikipedia.org/wiki/Volkswagen_Lupo

Graham

3-cylinder? Well, if you want real economy, an electric scooter with
SLA battery charged from a SMPS brick is about as far as you can go.

Best regards,
Spehro Pefhany

 

[René]

I think you mean the 3 CYLINDER Lupo. It has a 1.2 litre turbodiesel engine.
http://en.wikipedia.org/wiki/Volkswagen_Lupo

It is indeed a confusing name.
The "3 liter" is supposed to express the fact that it consumes less
than 3 litres / 100 km. It is a special edition of the Lupo with
lightened interior and skinny tyres.

The "real life" Priusses (Priae, Prii - whatever) we have here do
15...18 km to a litre (no documentation, asking real life owners on
local phora), a figure that is easily beaten by a average diesel car.

This is overall use. In city use (stop & go) the Prius may have a real
advantage.
I do like the hybrid technology - but I wait for the figures to
improve.

I can imagine e.g. a light 2 stroke diesel, operating in its most
efficient fixed rpm, driving a generator / accu combo; wheels driven
by electrics only - may have a better yield.

Somehow I distrust the factory milage figures. Makes me think of PMPO
power..

http://jalopnik.com/cars/news/classic-top-gear-the-prius-kinda-blows-buy-a-diesel-186004.php