I just called the 800 number below, and after a few automated questions ( basically you verbally state other, other, other, since your question does not fit any of their FAQ ) you get to a live person within 1 minute.

I explained to him there have been several other "Hybrid SUV's" on the market for at least 3 years ( and named Ford, Toyota, and Lexus ) and said GMC would only be correct if they made the distinction "First Full Size Hybrid SUV" on their web site. He said he understood, and was typing notes during my entire phone call and said he would forward the info on to the Web Developer. He asked for my address and phone number in case the Web Developer or anyone else had questions, and to document the call came from an actual person I guess.

So now I would appreciate others calling in and doing the same, so GMC doesn't just write me off as a lunatic. Thanks! -John

 

 

The website says it is the worlds first "two mode SUV".

The two mode does not refer to it being a full hybrid vs a mild, it refers to it being a full hybrid with a 4 cylinder engine or a full hybrid with an 8 cylinder engine. This SUV has variable cylinder management.

Cris

 

Go back and check the title bar again. It simply claims to be the "World's First Hybrid SUV".



I read their website description differently. I thought the two modes, were the two different transmissions. The "hybrid" mode, the power (EV and ICE) runs thru a CVT. The "gas" mode, the power (ICE only) runs thru a 4-speed automatic transmission. Apparently to eliminate the inefficiency of a CVT when cruising down a highway.

 

"Two Mode" refers to the way the transmission works. It's complicated but basically it operates in one mode at low speeds/light loads. Gearing is used to multiply electric torque, which the FEH does not do. It is said that you can really feel it pulling when in electric mode. At higher loads/speeds, it literally shifts via clutches and a (more effecient) direct connection between the ICE and the drive shafts is established.

As you can imagine, the primary mileage benefit is in city driving.

 

Our FEH/MMH's have an eCVT and not just a plain CVT such as is used on some normal gas-guzzling vehicles. We have planetary gears and not belts, etc.

So, my question is, do we suffer from the inefficiency problem when cruising on a highway, that the Yukon Hybrid is solving by having two transmissions?

 

I am wondering the same thing. I am also wondering if this is not some great invention (two transmissions) but just a means of avoiding a patent dispute. I always thought of Toyota's "Hybrid Synergy Drive" as a CVT that can accept two inputs at all speeds. Does their solution avoid having to pay Toyota royalties? If so is that the motivation?

Cris

 

I think there is not enough information from GMC to make the kinds of determinations we all want. Did you guys call customer service?

By the brief descriptions, it sounds just like the FEH/MMH.
However, GMC uses slightly differenent terms for things we ( the experts ) like to pick apart.

Truly a two-mode hybrid transmission ( to me and my understanding ) means there is a low gear for EV at zero to 40 MPH ( the FEH, Prius, etc ) and there is a high gear for EV at 41 to 80 MPH. ( something no current hybrid does. )

GMC does NOT say their hybrid can go EV at highway speeds.
So far, this is not consistant with other descriptions of "two-mode".
Their Hybrid sounds just like Ford's.... so far....

-John

 

Here is a better description NOT from GMC's web page:

"What sets this system apart from the popular Toyota hybrid arrangement is that the Tahoe can run as a continuously variable transmission (CVT) and an automatic through one of four fixed gear ratios. With their theoretically infinite ratios, CVTs are much better than conventional automatics at keeping engines spinning at the most efficient speeds, but at constant highway speed, that advantage can be nullified by the internal friction inherent to CVT operation. In hybrids, the energy loss can be even worse because the drivetrain must also spin an electric motor. The Tahoe, however, can switch over to a more-energy-efficient mechanical path (one of the fixed ratios in the automatic) to minimize wasted energy whenever possible. Whereas the Prius is always processing its power through the CVT, even at inefficient highway speeds, the Tahoe’s system is better and can simply bypass the electric motors and lock onto a gear."

After that being said, I still fail to see the advantage.
Tahoe/Yukon gets 40% better city, and 5% better highway.

My FEH gets 100% better city and 50% better highway compared to a V6 equivalent.

 

I know we all have noted that, just as an example, our tach's show our ICE rev'ing up to 4,000 RPM or more, when going up a hill and trying to maintain a highway speed (65 miles per hour?).

We have also noted that attempting to keep the RPM's down during such events, will help increase (or at least maintain) our fuel mileage.

Where I am going is, would it be a better design if our transmission could somehow "lock up" when on the highway? Kind-of like the way more modern cars will have their torque converter lock up.

It kind of reads that GM attempted to address this, by having a 4-speed auto for use when cruising at a steady speed on the highway. Though, I am not sure that such a drastic solution is the only solution.