At very slow speeds you are correct, which is why GM hybrids and HSD hybrids take off under electric power. Extending EV mode past a certain speed is pointless, for the power path reason I already mentioned.

Those same gasoline engine efficiencies you mention also apply to the EV mode power path. Since the Tahoe/Yukon is not a plug in hybrid every bit of energy to move the vehicle comes from the ICE, same as all non-plug in hybrids.

 

How so?

How long do you think a Tahoe/Yukon could drive at 30 mph on "free" regen power before forced regen kicked in?

Do you not agree that my power path is correct in the case of forced regen?

 

On my last 650 mile trip I did 30.1 MPH.

 

You guys can theorize all you want. I have done many (dozens) over the road tests, and in my 2005 Ford Escape Hybrid, I can get 10% higher MPG by doing a mile of EV, a mile of gas powered travel with background charging, followed by 1 mile of EV, repeat, vs. driving with the gas engine on full time.

This works very well in the 25-35 MPH range.
I've done this for 100 mile stretches, going in a complete round trip, so the effects of terrain and wind cancel. I've done it too many times to consider it a "fluke". The electrical losses are less than most people predict.

Doing this, my engine never gets very hot (140 degrees is typ.) so I suspect there are significant thermal savings.

HTH,
-John

Also, an engine doing two things ( moving the wheels, and a generator ) at the same time, is more efficient than an engine only moving the wheel, so, thus, you get more bang for each buck.

 

Since I assume you are not lying and not owning a 2005 FEH myself I have no choice but to defer to your experience regarding the FEH. Such results are a bit of a puzzle giving my understanding of how these vehicles work but I'll still defer to you as far as the FEH goes.

That said your experience with the FEH does not mean that the GM hybrids would operate the same way. The FEH lacks a conventional tranny which may account for some of what you are seeing? GM's dual-mode does offer a more traditional mechanical power path option so the results could be very different with the GM hybrids.

Bob posted some graphs that showed some odd behavior with his HSD equipped Prius. I'll try to find them when I get time...

 

And I totally get what you are saying. Gas powered ICE's are so incredibly ineffiecent, that there is a huge margin to improve on. So even with all the losses listed below going though the conversions ( which do exist, just in smaller magnitude ) an electrical drive for a portion of the time comes out ahead. What do you say about vehicles that are full time electric to the wheels, and have a small gas or diesel generator to charge batteries, and net way over 100 MPG?

Think about how peak power is used very briefly, and very infrequently.
People cruise with 10% of their ICE's power. Very inefficient.

Another observation, confirmed by the masses, is, Hybrids like Fords do better in mountain terrain than flat terrain. This goes against conventional thinking as well.

A normal car uses more gas on the way uphill, and less gas on the downhill.
Many hybrids use more gas on the way uphill, and zero gas on the downhill.
Net gain of up to 25% in many cases compared to an ICE only car.

 

No, most hybrids use more gas on the way uphill and regen on the downhill (or use negative gas, in math terms).

I often find myself using hybrid regen driving style in my Aston Martin. Doesn't do much good (better on the brakes though). Just wishing I were charging a battery with that kinetic energy I'm losing...

Oh, on the ICE efficiency, the ICE is most efficient at full-load (as John and others have mentioned), which is how hybrids try to use it when recharging the battery. This is why it is better to cycle the engine on-off-on during extended stops to run the electrical loads, then to keep it idling while running the load. A few short bursts of heavy loads are better than one long light load.

 

I think many people who say hybrids are only slightly better than gas cars, only compare them to running down the road under load.

Few people consider how many minutes, hours, miles, per day/year that hybrid cars have the engine ( or fuel ) cut off completely and hence get infinately better MPG that an equivalent size traditional car.

Driving down the Interstate at 70 MPH, my FEH is only slightly better than a regular Escape. It might be 1 or 2 mpg better in these cases. Not worth the cost and materials of that's all someone does.

However, my engine is off 20% of the TIME compared to a "normal" Escape.
And yes, I have data to prove it. A couple years back I installed runtime clocks on both my engine, and ignition. For every 1000 hours the ignition is set to "run" my gas engine runs for 800 hours. And the past 2 years I've done mostly highway driving. In city, it's more like 50/50.

 

I am with you fjungman, we need a GM HYBRID drivetrain engineer on here! I have done much of the same sampling of drive characteristics that you guys have. I have noticed that the "pulse and glide" works with this truck as well as a Prius! I am very surprised and the proof will be in this tank of fuel. I have been doing the P&G when I can but not extensively.

Let me back up just a bit. I had the Open Recall on the transmission controller #09241 done and I could swear it cut my mileage. So I started trying new techniques. I had a DIC average of 19.1 on this tank, so I started doing the P&G and EV where I can, I have the tank up to 20.2 on the DIC! That is the best I have seen by far and that improvement was inside of a single tank of gas!

I will close by posting a picture I put as an attachment in another post on this forum about the software logic regarding the 2-mode hybrid system. I will attach it again here.