## GM Two-Mode SUVs to Offer 40% Improvement in City Fuel Economy

##### 31 July 2007

The forthcoming Chevrolet Tahoe and GMC Yukon two-mode hybrids will offer a fuel economy improvement of approximately 40% in city driving compared to conventional models of the SUVs, according to GM.

The V-8 powered two-mode hybrids are combined with GM’s Active Fuel Management cylinder deactivation technology. The Tahoe Hybrid will go on sale in the fourth quarter of 2007 as a 2008 model, along with the GMC Yukon two-mode Hybrid. Pricing and production volumes have not been announced.

Because of its low- and high-speed electric continuously variable transmission (ECVT) modes, the system is commonly referred to as the two-mode hybrid. However, the system also incorporates four fixed-gear ratios for high efficiency and power-handling capabilities in a broad variety of vehicle applications. (Earlier post.)

During the two ECVT modes and four fixed-gear operations, the hybrid system can use the electric motors for boosting and regenerative braking.

In the first mode, at low speed and light loads, the vehicle can operate in three ways: electric power only, engine power only or in any combination of engine and electric power. When operating with electric power only, it provides all the fuel savings benefits of a full hybrid system.

The second mode is used primarily at highway speeds. In addition to electric assist, the second mode provides full eight-cylinder engine power when conditions demand it, such as when passing, pulling a trailer or climbing a steep grade. The second mode also integrates sophisticated electronic controls, such as Active Fuel Management, cam phasing, and late-intake valve closure, allowing even more efficient engine operation.

A sophisticated controller determines when the vehicle should operate in either mode of the 2-mode drive system. Input from the controller determines the necessary torque for the driving conditions and sends a corresponding command to the engine and electric motors. The engine and electric motors transfer torque to a series of gears in the transmission, which multiply torque similar to a conventional automatic transmission to propel the vehicle.

A 40% improvement is great news! Original estimates were 25%. A 40% improvement in efficiency should put their mpg estimates in the 20's--really good for a Tahoe.

It's well known that a number of people that visit here strongly dislike the existance of these large SUV's, but the more efficient they make them, especially the ones in this class, the better off we'll all be in the long run. A choice for efficiency is going to be offered where there wasn't one before. I just hope the added cost isn't too much of a detraction for customers.

Great, those monsters may reach 12 to 14 mpg instead of 9 to 10 mpg. A great vehicle to take the kids to school and the ball game.

Kudos to GM. I hope it meets these numbers.

These are great vehicles.
I had a chance to test drive a pre-production model. You can read my review here:
http://www.gm-volt.com/2007/07/26/its-big-its-tough-its-powerfulits-a-hybrid-gmc-yukon-hybrid-test-drive/

There is a market for huge SUVs as a special purpose vehicle. But, I think that the high cost of fuel will limit sales. Additionally, people are being educated by the facts that it takes lots of energy for the inefficient ICE to move all that weight and large frontal area down the road.

Still, it is good to see that GM is dealing with the mileage problem of huge SUVs. Every little bit helps. I wonder if Ford has a similar idea.

GM has been all talk and little action when it comes to improving fuel efficiency. I will wait till the EPA numbers come out, before I celebrate.

Anyway, with a electric motor assist, why do they still need a V8, wouldn't a V6 do the job? - like the Lexus LS600h?

This year's Suburban has mileage ratings of 15 city, 21 highway. Projecting the 2008 hybrid model will be rated at 21 city, 27 highway. This is based on improvements of +40% city; and only +25% highway estimates.

This is really very good mileage for the biggest, heaviest, and thirstiest, LDV sold in America.

Now that these vehicles can be built in great numbers it will be interesting to see if the actual vehicles with this drive train is reliable and comfortably powered, for the hauling and trailering applications for which people purchase such large vehicles.

As I recall, the drive train factory was being designed to produce about 400,000 such dual-mode drive trains per annum.

The drive train is prepared for the addition of a larger battery as well, so PHEVs spun off this are a simple upgrade. Such a vehicle might allow for a downgrade of the 5.3 liter V-8, to a combo of a 3.6 liter V6 and the electric motor, without hurting torque for towing applications, I would suspect.

That might be a vehicle with 18 mpg city and 26 highway upgrade to a dual-mode hybrid of 25 mpg city and 32 highway, BEFORE PHEV upgrade and substitution of electric mpg equivalents.

SM:
A V8 is still needed since the vehicle will still be designed for towing applications. I'm not an authority on the mechanical workings of their 2-Mode Hybrid system, but it seems that when they were thinking of using this system in their large SUV's, they wanted to employ something that saved fuel where it could, yet still enabled the vehicle to do all of things a traditional Tahoe could do. Hopefully they have the bugs worked out.

To the anonymous poster: You're off by 30%+!

2006 Yukon EPA ratings are 12/17 City/Highway with the new method (old method was 13/18). A 40% increase will get them closer to 17 city and the highway rating should also improve if it only uses 8-cylinder mode as conditions dictate (most highway driving is not at full-power).

We borrow our neighbor's Suburban (same model, different name) when we have 6-8 people/kids traveling (plus baggage), by taking one vehicle like this instead of two regular cars, we're effectively getting 34MPG!

Since 2004, when Oil prices climbed $40 / barrel, the sales of SUVs were declining steadily. Oil Prices hit records in 2005 & 2006 because of Hurricanes and Wars. But today, it has hit another high (highest closing price) without any such event.$ 78.21 / barrel is todays closing price.
I dont think the Tahoe/Yukon Hybrid is going to help either.

It will be better, if GM can apply this system in Impala, Malibu, Aura, G6 like vehicles.

Meanwhile Toyota reduced price of Prius by \$1,200 and expect more people to go towards it.

Max:
I tend to agree that a 2-Mode Hybrid system might be more of a help in mid sized vehicles such as the ones you mentioned. The price decrease on the Prius will also help to move more of them also. However, people that need a vehicle for towing and want to see better fuel mileage to boot, can now look towards these Hybrid Tahoes. In this scenario, as good of a vehicle as the Prius is, it is just not going to cut it.

This year's Suburban has mileage ratings of 15 city, 21 highway. Projecting the 2008 hybrid model will be rated at 21 city, 27 highway. This is based on improvements of +40% city; and only +25% highway estimates.

You're using old EPA numbers. The current ones are here -- 14/20/16. It's not going to get anywhere near the numbers you're using.

Hey, who doesn't think that we American are idiots for having so many of these monsters on the road, endangering others, using far too many resources, chewing up road surfaces, and fouling the air?

But as there are so many, and the fashion has been set, then I am all for reducing their oil consumption and their carbon footprint. I just hope that the Big Three work as hard to make other vehicles as attractive, rather than leaving us in this Heavy Steel arms race we have been in since 1990. Such foolishness....

I think a 40% improvement is a little bit too optimistic. I doubt they will achieve that big of an improvement.

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