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Hybrid Gas Mileage Good? Bad? As Expected?
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Comments
Why? All that the throttle position does is increase RPM. That's why I'm confused. Regardless of the gearing, for ever revolution of the engine, the gas is sprayed into the cylinder, and spark plugs fire. So for any given revolution of the engine, the same amount of gas is sprayed into the cylinders, regardless of whether you're at idle or climbing a hill.
Or does the fuel injectors spray a greater quantity of gas into the pistons if the engine is under a load?? That would be the only way that the extra load would mean more gas is used for a constant RPM.
My understanding is that it's only the increased RPM that makes gas usage higher. And I'm not talking about MPG...miles per gallon, but gallons used per revolution.
The mpg at idle is zero, but I'm trying to calculate how much gas is actually expended at idle, so I'm calculating a gallon per RPM.
But how do you think it increases rpm?
Increased throttle position increases the amount of fuel/air injected into the cylinder, hence more torque is generated, and the rpm increases (assuming there is no load on the engine keeping it from increasing in rpm).
"So for any given revolution of the engine, the same amount of gas is sprayed into the cylinders, regardless of whether you're at idle or climbing a hill."
No.
Forget hills/idle/etc. Picture two identical cars, identical gearing, identical EVERYTHING, both driving down a level road at the same exact vehicle speed and engine rpm. Since both cars have the same engine rpm, they should both be getting the same mileage, right?
But what if car 'A' is pulling a 5000 lb. trailer? Under your theory, they are identical vehicles with identical engines turning identical engine rpm so they should get the same mileage.....do they?
So how do you calculate how much gas is spent when idling?
Almost there.
You put more gas into the cylinders to get MORE power at the same rpm.
Torque (and by extension, horsepower) is not fixed at a particular rpm. When you look at a dyno sheet which plots torque (or hp) vs. rpm, these curves are always based on WOT (Wide Open Throttle) conditions. A dyno sheet of power vs. rpm would look much different (same basic shape but lower power/torque) at part-throttle conditions.
In other words, a particular engine at 2000 rpm is NOT always developing 'x' amount of torque (or hp); it varies depending on throttle position. The reason why car 'A' must dip further into the gas when towing that 5000 lb. trailor is because, at 2000 rpm, more torque is needed to lug that trailer around.
"So how do you calculate how much gas is spent when idling?"
I've absolutely no idea. You would have to get your hands on the data used to program the engine management computer in your particular car to determine how the programmed fuel flow rate was set for idle conditions.
You could approximate this (if you just really REALLY had to know):
1. Fill your tank and drive home.
2. With the car in the driveway, top off the tank from a gas can.
3. Idle the car for some set length of time (the longer the time, the more accurate the calculation).
4. At the end of the time interval, shut off the car and re-top off the tank keeping track of exactly how much fuel used. This should give you an idea of the gallons/hr fuel flow rate at idle.
If you do this in a garage, make sure you leave the garage door open. :surprise:
Of course, this will all prove somewhat difficult to do with a hybrid for obvious reasons.....
Good question.
Back to the car going down the road at 2000 rpm (at, say, 50 mph). The car will require SOME amount of hp to just maintain 50 mph (say 25hp). Which means that, AT THAT throttle position, at 2000 rpm, the engine is developing 25hp.
Then you step on the gas. More fuel/air goes into the cylinder and AT 2000 rpm, the engine is now making more torque, and hence more power (perhaps now it is making 75hp).
That additional 50hp must DO something. The added force applied to the top of the piston is translated into additional torque by the crankshaft. That additional torque is transmitted via the tranny/axles to the wheels where the added torque accelerates the vehicle (F=ma or Force = mass x acceleration).
If the car was on level road and the power requirements to maintain speed was 25hp and now the engine is developing 75hp, then the excess power is used to accelerate the vehicle. RPMs increase.
If the car has started up a hill, then the power requirements to maintain speed may increase from 25hp to 75hp. So, the gas pedal goes down, until the engine is now making 75hp. Since the energy produced is balanced by the energy requirements, there is no excess power and the speed remains the same.
I hope this helps.
I hope you are all enjoying your hybrids. I could made 56 mpg on 87 miles today.
Any uneducated driver can get into a Hybrid and produce bad results. But if they OWN the car and are paying for the gas out of their OWN POCKETS and the car payment out of their own pockets, they are smart to learn to maxmize the MPG of the car using the tools provided by Toyota."
Pardon me if this is an obvious question, but if a driver can achieve good numbers by following Toyota guidance (as perceived by the efficiency displays in the Prius), why can't Toyota program the Prius computer to make those same efficiency decisions?
I realize that some of the techniques are driver only (timing the stoplights, for example), but EV mode? Why not at least put in a button to allow the user to force the car into better MPG?
Normal driving - some hard acceleration in city, under 75mph highway: 27 - 28 mpg
Extreme driving - Aggressive acceleration in city, 80mph and up highway: 22mpg
Conclusion: even driving this vehicle very hard, my Ford Escape Hybrid can give fuel economy better than the Ford Escape XLT, which according to Ford is a similar driving experience from the point of view of acceleration etc. The Escape Hybrid is probably a little less sporty, in truth, but it does feel to me much quicker than the Honda CRV AWD I drove previously (which gave me under 20mpg in hard driving, by the way).
My full review ...">link title
Mileage report:
Lifetime average is just under 60MPG.
2004 I was learning my new car and how to maximize efficiency and averaged mid 50's.
2005 Fine tuned what I was doing and applied it to rediculous measures and averaged 65MPG. Had one tank go 941 miles and calculated to 69.2MPG.
2006 Driving more "normal" now and mostly freeway. Still average 57-58MPG and +700mile tanks this winter.
Spring is here with warmer temps and had a couple 60MPG tanks.
I live in N.Georgia in the "foothills of the foothills" of the Blue Ridge mountains. I drive non-rush hour traffic.
The car have been nothing less than fantastic.
Thanks,
Chintan Talati
Corporate Communications
Edmunds.com
2004 Honda Civic Hybrid CVT (AT)
With 1000 miles on odometer I'm averaging 30.6 mpg.
As Goldilocks would say... "... it's just right!"