But even when I'm accelerating, unless I'm REALLY PUSHING IT, I don't see that mine has gone wide open throttle. The RPM guage doesn't creep above 2500-2800 or so for a typical acceleration from 0-55. So if the most efficient way to accelerate is WOT, why doesn't the ECU go ahead and crank the engine to 5000-6000 RPM whenever I accelerate which is what I would assume is nearly WOT?

I think thats what I'm confused about.

 

Tim, I'm sure Willard has good intentions, but WOT and good FE have nothing in common. I used wide open throttle in my racing days, but I was not looking for FE.

Willard and I strongly disagree on FE, but if he can get better MPG with WOT, I'd like to see his numbers. My Miles To Empty below indicates I'm getting better than Willard's Prius rated at ~60 MPG city. I think he said he was getting around 46mpg. Most of you may not understand how I get the mileage I do, but I'm trying my best to explain. It does not have to be a driver who drives so slow to **** everyone off.

This WOT thing Willard has brought up IMO, is BS until he can show his numbers. Good luck Willard, because I would like to improve 47+mpg with my FEH. Going to WOT is crazy IMHO!

GaryG

 

There is so much non-factual information in this discussion it needs to be corrected.
1. Peak torque is NOT at WOT, peak power is at WOT. Gary, in post 22 of this thread provided a curve that shows peak torque is around 4,500 rpm, which also corresponds to values reported in reviews such as Car & Driver for the FEH.
2. Peak power for the FEH is around 6,000 and is limited by the engine controller.
3. A presentation by John Miller (see slide 42), gives the engine performance map for the Prius. Peak fuel economy is around 2,000 rpm. The torque is seen to drop off near WOT, just like the FEH. The slide also shows the engine control strategy for the Prius, so it should be evident why you see the rpm behavior you see when you accelerate. See http://www.engin.umd.umich.edu/vi/w4...Miller_W04.pdf
4. Ford, for what ever reason, has not published the engine performance map for the FEH, but it should be similar, but scaled.
5. Any good engine text book will show that: efficiency decreases at high rpm due to increased friction losses and at low rpm due to increased heat loss to cylinder walls Where people discussing this thread have gone wrong is apparently confusing volumetric efficiency with friction losses. Engine “breathing” is just one part of friction losses. Also, efficiency increases with engine size due to reduced heat losses and with compression ratio due to higher thermal efficiency.
6. This behavior can be seen in a study done by Argonne National Labs for the Prius, see the last slide (tabulation of data) and the 3rd from last slide plotting the efficiency as a function of engine power.
7. Experienced hypermilers have found the most efficient operating points for the engine are those with low engine speed and high load, NOT WOT.

 

Did you really intend to state that peak engine torque can be reached without WOT?

Pardon me, but that seems highly improbable, even impossible.

Okay, the throttle is at the 1/2 way point, the engine is at 3000 RPM under load in second gear at 45 MPH.

Now I go WOT throttle. What engine parameter now changes FIRST.

The pumping losses have just be dramatically reduced via removing the airflow restriction, limitation, of the throttle plate. Not to tout K&N in any way but just what load of poles do you think K&N has been peddling all these years?

And by the way, I have never before seen engine breathing, pumping losses, lumped in as frictional losses. Friction, look it up.

 

"..., but WOT and good FE have nothing in common...."

Sorry, but since when?

Now, certainly, WOT is NOT to be used to reach the BEST FE, but if you have need to produce a high level of torque while remaining mindful of FE, WOT will always win the day. An otto engine is at its most efficient at WOT insofar as FE is concerned provided you have need of that level of power.

 

Okay if what you are saying is that the most FE way to produce full torque on an atikinson engine is WOT, that makes some sense to me. What the FEH would be doing in normal driving is finding the appropriate balance of engine torque, motor torque (developed by converting some of the engine torque through the generator, and some from the battery as a boost if necessary) to provide the total torque to the wheels necessary to accelerate the vehicle at the requested rate at the best fuel economy.

WOT would only be used and be most efficient IF the driver is requesting MAXIMUM acceleration.

Is that what you mean?

 

WOT gives you the most horsepower per gallon.
Thus, it is excellent for fuel ecomony, if you have a need/use for maximum horsepower. So mathmatically, WOT is BEST for fuel economy!!!!

However, the maximum horsepower is usually ( almost always ) more than is requested for normal driving. If you were doing a sled pull with your FEH, I'm sure no one would disagree with WOT being the best.

Directly from Ford:

"Owners at higher altitude will see increased fuel economy due to the fact that the throttle is at WOT more often, and closer to WOT all the time to achieve the same air/fuel ratio."

Does that clear things up???

-John

 

Yes, completely, thanks muchly.

That's exactly why I have been proposing taking along a genset when traveling a fairly long distance on the freeway wherein the hybrid system is currently handicapped.

The genset engine would use the extraordinarily high efficiency miller cycle and be of a capacity just marginally capable of (re)charging the hybrid batteries at their maximum charge rate. The genset would "kick-in" at WOT just prior to the hybrid batteries being discharged to the point wherein the ICE would begin to be used for same.

So for freeway driving, when there is little or no opportunity for the use of regenerative braking to recharge the hybrid battery, the genset would be used instead. Since it would always run at WOT and with a constant load, or very close thereby, it's Supercharger could be of a fixed speed.

The genset could run on CNG, Compressed Natural Gas, taken directly from your home supply.

 

OT, but maybe pertinent.

'...When I already have my into the throttle (maybe 1/8??).."

Full light-throttle doesn't really fully describe the circumstances wherein a downshift delay seemingly occurs.

On FULL lift throttle followed quickly by a need to accelerate moderately or rapidly....and assuming a lower gear ratio at the onset:

The engine RPM will drop to idle as the engine/transaxle ECU commands an upshift.

Now suppose you quickly re-apply pressure to the gas pedal having been in the FULL lift-throttle "state" for just long enough for the upshift command to have been issued.

The engine being at idle results in a very low pumping rate of the fixed displacement ATF pump so once the currently in-process upshift is completed the "reserve" ATF pressure supply will have been exhausted.
So now the succeeding downshift command cannot be issued until enough time has expired for the ATF pump to have replenished ATF pressure, enough to fully and firmly seat the downshift clutches which are without doubt about to be asked to endure, sustain, a fairly high level of engine torque, once the DBW is allowed to open the throttle.

Obviously there are other sequences that might result in this same senario. Say cruising with a light, 1/8 gas pedal position, and an absolutely "normal" upshift has just begun. The DBW system drops the engine RPM to idle to more seemlessly and smoothly accomodate the upshift, but now you put your foot into it a large bit more.

Two shift sequences, an upshift followed quickly by a downshift, with the gas pedal lightly applied at "entry".

And keep in mind that with DBW the gas pedal position will not necessarily be indicative of the throttling opening. There is a bit of confusion about this for vehicles with CVT, Continuously Variable Transmissions, especially so with the wildly different, unique, CVT in many of the new hybrid drive vehicles.

With a CVT any position of the gas pedal that indicates a desire by the driver to accelerate might result in WOT engine operation. If the CVT can accomodate the "gear" ratios involved given the current roadspeed and engine RPM WOT will result in eliminating pumping losses due to throttle valve flow restrictions and thereby the most optimal FE. Keep in mind that WOT means climbing most rapidly to maximum engine RPM, not continuously operating there.OT, but maybe important: