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#16 of 41 Re: Can someone enlighten me a little? [larsb]
Dec 22, 2004 (4:43 pm)
Same questions with a 2002 Prius (2004+ is similar, with differences noted below. Any hybrid using a power split device like Toyota or the Ford Escape Hybrid will have the same basic design features).
Q: Is it true that whenever you step on the brake, the gas-engine shuts off?
A: Depending on conditions, yes this is true. The ICE (internal combustion engine) will continue to run if (a) the battery needs additional charging (b) the engine and catalytic converter are not warm enough to keep emissions down (c) the A/C compressor is needed for cooling or defrosting (the 2004+ Prius has an electric air conditioner so this does not apply).
Q: Does the engine shut off when going down a big hill?
A: Depends on your speed. Above about 42 MPH the Prius' ICE must turn to keep the RPM of the electric motor from exceeding its redline. However, fuel and spark may be cut off and the engine allowed to turn from the momentum of the car. Some refer to this mode of running as "turbo stealth" since low speed electric running is called "stealth mode".
Q: Let's say you're riding on the freeway for a while and the battery is now fully charged, will the gas-engine ever turn off during the freeway drive?
A: For the reasons stated above, the ICE will not stop turning, but fuel and spark could be shut off if the electric motors are providing sufficient power to overcome wind and road resistance, etc.
Dec 24, 2004 (10:16 am)
"Because you eliminate the air-intake losses around the trottle"
"Sounds like a nice thoery. Still doesn't explanin why it burns twice the fuel."
It burns twice as much fuel, because the engine is spinning twice as fast, but the specific fuel ratio (gasoline burned/energy produced) is lowest at Wide Open Throttle. WOT, followed by coasting to 0, and then WOT again, et cetera - is what drivers use to set those MPG World Records. Why? Because opening the throttle removes the air-intake restriction & improves efficiency.
Look, I don't have to justify myself.
My 91 mile per gallon lifetime MPG speaks for itself. I wouldn't have that if using WOT was the wrong thing to do.
#18 of 41 Re: [electrictroy]
Dec 24, 2004 (4:25 pm)
I've heard that theory over at Insight Central as well, that's why I did the test on post #8 myself, to settle once and for all.
I also did the test with a 3 mile run and the outcome was the same.
WOT will burn twice the fuel over the same distance and finishing speed, vs very light throttle.
Your 91MPG LMPG is fantastic and indeed you should be proud of that achievement.
I'm also happy with my 59 LMPG in my HCH with my family of 5.
Jan 06, 2005 (10:35 am)
Okay I conceed.
But your slooooo-leeeee accelerate to 55 approach is nowhere near as much fun as my burn rubber & full-throttle-to-55 approach.
#20 of 41 Re: [electrictroy]
Jan 06, 2005 (6:54 pm)
___The batteries from a slow accelerator will last far longer and that is an expensive $4,000 proposition for 15 - 20 seconds worth of fun about 20 Xís a week
___Whose Hybrid would you rather buy used? The 30 - 50 second to 60 mph driver or the 12 - 18 second to 60 mph one? The fun as you and I know is in the long term use of the game gauges, not ramming her home for a 0 - 60 mph sprint in 12 - 18 + seconds. That isnít all that fast if you know what I mean
___By the way, welcome back.
___Wayne R. Gerdes
Jan 07, 2005 (10:47 am)
"___The batteries from a slow accelerator will last far longer "
Yeah like I care. My battery hardly ever gets used (I drive a steady speed for 2 hours each day with no battery assist)... my battery will last forever.
When my Insight's engine finally dies at 300,000 miles, I plan to tear apart the battery & use the D-cells to power my electric model airplanes.
Jan 11, 2005 (8:39 am)
"I did the test on post #8 myself, to settle once and for all. WOT will burn twice the fuel over the same distance and finishing speed, vs very light throttle."
Really? So what were the actual MPG results? ~40 mpg WOT vs. ~80 mpg slow ("twice the fuel")? I find that impossible to believe.
Also when you did the WOT test, what shift pattern did you use? 1-2-5?
#24 of 41 Re: [electrictroy]
Jan 11, 2005 (4:22 pm)
Here are the results of my test, this is a repost from June 04, and I am driving a CVT:
80 Degree high humidity Possibly 90% on the edge of rain,
Engine completely warmed up for about 1/2 hour of driving,
Battery Pack (SOC) is 4 bars off of full (normal full charge),
No A/C or any other accessories, Windows up.
The 1st test was on a straight strip of road that has a linear slight incline.
I did a series of "Control" tests to measure the road itself and this is what I found:
The road chosen is 1/2 mile long.
The HCH maintains 50MPH with FCD held at 44MPG.(40 + 1 bar) on ascent.
Other way around on the decent it maintains 50MPH at 84MPG.
Hopefully that will show the grade as it is not level.
I did a series of tests to measure fuel consumed going 0-50 on ASCENT ONLY.
FCD is reset at the moment each run was started.
Once 50MPH is reached the FCD is adjusted to 44MPG to maintain speed.
MPG is measured at the 1/2 mile mark. Tests were ran 3 times, each had about the same results.
This is what I measured:
Full throttle: 0-50 in 10 seconds 19MPG
FCD held at 20MPG during acceleration: 0-50 in 31sec 25MPG
Very slow acceleration: 0-42 in 56 sec (Reached 1/2 mile) 30MPG
If anyone takes the time to do these tests themselves they'll see similar results. Also keep in mind that the battery was less depleated after a gradual run, so it had less to recharge.
Jan 13, 2005 (8:57 am)
Your test strip is too short. We're talking long-term trends here, because even though full-trottle will *initially* burn more fuel getting to 55, you will spend more time (~20 seconds) in the lean-burn >80mpg mode, and that leads to *higher overall* mpg.
Also, it says full throttle but it doesn't say what gear? "Drive" "Second" or "Low"?