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> The thing I find interesting is that my car weighs easily enough to crush
> every single bone on your body... and yet it's not actually that hard to
> push it along a road.
...
> (I guess my wheel baring work really well?)
I guess they design them to be pretty good :-)
> (Also curios is the fact that the car doesn't accelerate when you drive it
> down a hill... You'd think it would.)
Press the clutch and start off at 5mph so as to avoid any air drag. It
should accelerate then.
> I would think this electric motor trickery probably also saves fuel on
> low-speed manovers like trying to park. [Think how much you have to rev
> the engine to make a car move that slowly...]
Ermm, my car moves just by lifting the clutch gently, no need to rev at all.
> ...OK, so maybe it wasn't exactly 10^(-6). But it worked out to be some
> absurdly small figure anyway.
IIRC you meant that amount per revolution of the engine, not per minute!
> I've always wanted to know... An engine is a mechanical device. So why
> does temperature have any effect on anything?
Things expand with temperature, an engine is designed to run smoothly at
it's operating temperature, below that there is a lot more friction.
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Invisible wrote:
> The starter motor is designed to convert electric to kinetic. The
> alternator is designed to convert kinetic to electric. I'm musing over
> whether either device can do the *opposite* job. :-P
If you essentially disengage the safeties and get them hooked up right,
yes. But since the starter motor is designed to start a car that isn't
running, there are (for example) no mechanisms to let you mesh the gears
when the motor is already running. Try turning the key when the car is
already running and you'll see what I mean.
Similarly, the generator (if you have one) really only kicks in when
you're already going more than about 20MPH, and the alternator does
funky things to keep drawing power even at low RPMs without stalling you
out.
> doesn't repeatedly starting up a petrol engine waste fuel anyway?]
Depends on whether it's carburated or fuel-injection. With fuel
injection, there's no "ramp up" to get the fuel from the tank to the
engine, no already-carburated fuel sitting in pipes and then going to
waste or evaporating, etc. It used to be starting a car used 90 to 300
minutes worth of idle-speed fuel. Nowadays, it uses maybe 2 seconds
worth, or less with cars designed to turn on and off like the hybrids.
> I've always wanted to know... An engine is a mechanical device. So why
> does temperature have any effect on anything?
It's a mechanical device that derives power from the difference in
temperature between the inside and the outside.
In the same way, a balloon zings around the room when you blow it up and
let it go, but falls to the ground when it runs out of air.
--
Darren New / San Diego, CA, USA (PST)
Helpful housekeeping hints:
Check your feather pillows for holes
before putting them in the washing machine.
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>> (Also curios is the fact that the car doesn't accelerate when you
>> drive it down a hill... You'd think it would.)
>
> Press the clutch and start off at 5mph so as to avoid any air drag. It
> should accelerate then.
Oh, it *does* accelerate... just... not very much. I mean, if you point
a *bicycle* downhill, it takes off like a rocket. And it doesn't even
weigh much! But a much heaveir car... doesn't seem to pick up speed very
much.
>> I would think this electric motor trickery probably also saves fuel on
>> low-speed manovers like trying to park. [Think how much you have to
>> rev the engine to make a car move that slowly...]
>
> Ermm, my car moves just by lifting the clutch gently, no need to rev at
> all.
Is your car diesel by any chance?
>> ...OK, so maybe it wasn't exactly 10^(-6). But it worked out to be
>> some absurdly small figure anyway.
>
> IIRC you meant that amount per revolution of the engine, not per minute!
Right. So given that there's roughly 10^3 revolutions per minute, that
would be about 10^(-3) L per minute. ;-)
>> I've always wanted to know... An engine is a mechanical device. So why
>> does temperature have any effect on anything?
>
> Things expand with temperature, an engine is designed to run smoothly at
> it's operating temperature, below that there is a lot more friction.
Ah, I see. That would make sense...
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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Invisible wrote:
> Actually, you laugh, but I did see a report about a car that has a giant
> motor inside it that drives the wheels at low speeds, acts as a starter
> motor to start the petrol engine when the car is moving fast enough, and
> acts as an alternator to charge the batteries thereafter. Basically the
> petrol engine only runs while the car is doing more than 20 MPH. The big
> advantage being that waiting at traffic lights uses no fuel.
>
> [Actually, having computed that my car uses 10^(-6) L of fuel per minute
> even when it's flying down the road at 75 MPH, I wonder just how much
> fuel it can possibly be wasting on tickover? And also, doesn't
> repeatedly starting up a petrol engine waste fuel anyway?]
>
I'm having trouble with that math, but it could be that I haven't looked
at a diesel car in a while. My sisters car got, lets say 35 miles per
gallon when running at mostly highway speeds. I'm probably
underestimating it a bit, it was a small car. At 70 mph, that's 2
gallons of fuel an hour. 3.78 liters in 30 minutes, gets .12ish liters
per minute.
Unless you are coasting all the way downhill in both directions.
> Last I heard the car never came to market. They were still playing with
> the control software to try to figure out the most optimal algorithms...
>
They have gotten it working, the Toyota Prius does just that. It can run
on the electric motors up to around 35 MPH, and cuts the petrol engine
off when ever it doesn't need it. The batteries for the electric system
charges off of both the petrol system and a regenerative braking system.
What's really odd is riding in one of these cars when the petrol engine
cuts off at highway speeds. The car just decides that going down hill is
easy, and the driver is braking anyways, so who needs the engine?
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4852b62f$1@news.povray.org...
>
> Oh, it *does* accelerate... just... not very much. I mean, if you point a
> *bicycle* downhill, it takes off like a rocket. And it doesn't even weigh
> much! But a much heaveir car... doesn't seem to pick up speed very much.
>
Ask Galileo :-)
Marc
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>> [Actually, having computed that my car uses 10^(-6) L of fuel per
>> minute even when it's flying down the road at 75 MPH, I wonder just
>> how much fuel it can possibly be wasting on tickover? And also,
>> doesn't repeatedly starting up a petrol engine waste fuel anyway?]
>>
>
> I'm having trouble with that math, but it could be that I haven't looked
> at a diesel car in a while.
Don't worry about it. I plucked 10^(-6) L out of the air. My point was,
during recent calculations it showed up that just coasting along uses
surprisingly little fuel. (I calculated that the amount of fuel injected
into each cylinder is drastically less than 1 drop. Which, obviously, is
impossible. The fuel would have to be vapourised or something, otherwise
surface tension would simply prevent you injecting such an absurdly tiny
volume.)
My [petrol] car can to 75 MPH at roughly 45 MPG. Let's do some math...
75 miles/hour = 1.25 miles/minute.
45 miles/gallon = 204 miles/litre.
204 miles/litre = 0.0049 litre/mile.
1.25 miles @ 0.0049 liter/mile = 0.0061 litre.
So we have roughly 6.1 * 10^(-3) L/minute. That's 6.1 mL per minute.
That's, like, one teaspoon of fuel per minute, while rocketing along at
75 MPH. What the hell the engine uses while idling has surely got to be
even smaller than this...
>> Last I heard the car never came to market. They were still playing
>> with the control software to try to figure out the most optimal
>> algorithms...
>>
>
> They have gotten it working, the Toyota Prius does just that. It can run
> on the electric motors up to around 35 MPH, and cuts the petrol engine
> off when ever it doesn't need it. The batteries for the electric system
> charges off of both the petrol system and a regenerative braking system.
>
> What's really odd is riding in one of these cars when the petrol engine
> cuts off at highway speeds. The car just decides that going down hill is
> easy, and the driver is braking anyways, so who needs the engine?
The reporter I saw remarked how eerie it is when you pull up at some
traffic lights and the engine goes silent...
Personally, it still kinda weirds me out that when a train is about to
get moving, it makes this loud whirring noise, and starts moving, and
then the whirring shuts up and the train accelerates MORE. o_O
[Of course, the noise you can hear is actually the hydraulics for the
brake system or something - it has nothing to do with the more or less
silent motors that actually drive the train along.]
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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Orchid XP v8 wrote:
> 45 miles/gallon = 204 miles/litre.
PWN3D!
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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Let's try that again, shall we?
75 miles/hour = 1.25 miles/minute.
45 miles/gallon = 9.89 miles/litre.
9.89 miles/litre = 0.101 litre/mile.
1.25 miles * 0.101 liter/mile = 0.126 liters
So now we have 0.126 liters/minute - a considerably larger value. (About
a third of a coke can.) Still surprisingly small given the insane
velocity involved.
(For what it's worth... I'm currently debugging a partial predictive
matching engine that keeps telling me that symbol A currently has a 130%
probability of being seen next. *sigh*)
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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On Fri, 13 Jun 2008 21:18:54 +0200, "m_a_r_c"
<jac### [at] wanadoo fr> wrote:
>
>4852b62f$1@news.povray.org...
>>
>> Oh, it *does* accelerate... just... not very much. I mean, if you point a
>> *bicycle* downhill, it takes off like a rocket. And it doesn't even weigh
>> much! But a much heaveir car... doesn't seem to pick up speed very much.
>>
>Ask Galileo :-)
>
No one expects the Spanish inquisition :)
--
Regards
Stephen
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Orchid XP v8 wrote:
> Oh, it *does* accelerate... just... not very much.
You need bigger hills. Come down over the Pacific Divide some time, and
you can brake to 5MPH and be up over 80 MPH in half a mile.
--
Darren New / San Diego, CA, USA (PST)
Helpful housekeeping hints:
Check your feather pillows for holes
before putting them in the washing machine.
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