VW and Continental Partner on Hybrid Power Electronics
Toyota Rolls Out the New Camry and Camry Hybrid

GM Formally Introduces Mild Hybrid Saturn VUE and Two-Mode Hybrid Tahoe

A cutaway view of the VUE hybrid. Click to enlarge.

GM used the North American International Auto Show to debut its mild hybrid 2007 Saturn Vue Green Line (earlier post) and the 2008 Chevrolet Tahoe Two-mode Hybrid (earlier post), featuring the first application of a two-mode full hybrid system in an SUV. GM also announced that it would apply the two-mode system in an upcoming hybrid version of the Cadillac Escalade.

The 2007 Saturn Vue Green Line Hybrid Belt Alternator Starter (BAS) system features a electric motor/generator mated to a 2.4-liter VVT four-cylinder engine and 4T45-E four-speed transmission powertrain that delivers an estimated 27 mpg city and 32 mpg highway (29 mpg combined)—a 20% improvement in combined fuel economy compared to the conventional VUE with a smaller and less powerful 2.2-liter engine.

The Vue Green Line’s hybrid system provides engine shut-off at idle, fuel cut-off during deceleration, electric motor/generator assist during acceleration and the capability to capture electrical energy through regenerative braking. The system consists of six elements:

  • The electric motor/generator unit that replaces the alternator, and is capable of 156 Nm of auto-start torque;

  • Engine-coolant cooled power electronics that control the motor/generator unit and provide 12-volt vehicle accessory power;

  • A Cobasys NiMHax 36-Volt NiMH hybrid battery pack capable of delivering and receiving more than 10 kW of peak power;

  • An engine control module;

  • An engine accessory drive with new, dual-tensioner assembly and cord belt that enables transfer of motoring and generating torque;

  • Hybrid-enabled Hydra-Matic 4T45-E electronically controlled four-speed automatic transaxle that includes an auxiliary oil pump and unique hybrid controls.

In motoring mode, the hybrid system quickly restarts the gasoline engine upon brake pedal release and provides momentary acceleration assistance as needed. The vehicle’s 12-volt accessory power also is generated in this mode.

In the generating mode, the hybrid system is used to provide both 12-volt accessory power and power to charge the battery pack. To perform these functions, the engine is used to power the motor/generator unit, which then provides a three-phase electrical output. In this mode, the energy required to drive the engine may come from either gasoline when accelerating, or the kinetic energy of the moving vehicle when decelerating with the fuel cut off.

The Vue’s hybrid system will cost less than $2,000 and the full vehicle price will start at less than $23,000.

For the 2008 Chevrolet Tahoe Two-mode Hybrid, GM paired the two-mode hybrid system with a 5.3-liter Vortec V8 that also features GM’s cylinder deactivation system, Active Fuel Management (earlier post).

Layout of the two-mode hybrid system in the Tahoe. Click to enlarge.

GM expects the two-mode hybrid to deliver a 25% improvement in combined fuel economy over the 20 mpg expected from the non-hybrid counterpart (i.e., an estimated 25 mpg US for the full-size SUV). The Tahoe Two-mode Hybrid will go on sale in 2007 as a 2008 model, along with the GMC Yukon Two-mode Hybrid. Pricing and production volumes have not been announced.

The two-mode hybrid system (earlier post) derives from the technology GM applies in its heavy-duty hybrid systems for transit buses, and is being co-developed by BMW and DaimlerChrysler for application in light-duty vehicles.

The two-mode system uses two 60kW motors coupled to two gearsets and is designed to provide a more flexible range of operating power, control and efficiency in both city and highway driving than obtained with a single-motor implementation.

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. In this mode, one motor acts as a generator, while the other provides drive (motor) power.

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. In this mode, In the second, both motors selectively operate in motoring or generating modes depending upon the vehicle speed.

The second mode also integrates Active Fuel Management, cam phasing, and late-intake valve closure for more efficient engine operation in addition to the electric support.

The two-mode system is designed to fit within the approximate space of a conventional automatic transmission—a form-factor advantage compared to single-mode systems that rely on larger electric motors.

The controller determines when the vehicle should operate in either mode of the two-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.

A 300-volt battery pack provides electric power for the system.

One of the intended design advantages of the two-mode system is the ability to package it in a variety of form factors for application in a range of vehicles.

Our hybrid strategy will not be confined to small cars or a limited number of vehicle architectures. Rather, we will offer sophisticated hybrid technology in a wide range of vehicles, and give customers what they’ve always wanted... choice.

In addition to the technologies themselves, the ability to haul large numbers of people in hybrid vehicles is going to be a competitive advantage for GM as we enter the hybrid segment in earnest.

We’ve focused our early efforts on large vehicles—“people haulers” like transit buses...and utility vehicles such as the Chevy Tahoe and Saturn Vue. Why? Because that’s where the most volume is, that’s where the most fuel is consumed...so that’s where our hybrid technologies are able to do the most good for the greatest number of customers.

—Mark LaNeve, Vice President of Vehicle Sales, Service and Marketing for GM North America

The full-size SUV sector is also facing erosion in the market, partly due to concerns over fuel economy, and that erosion is adding to GM North America’s financial pain. Bolstering the sector is of stated strategic importance to GM, which is also emphasizing its E85 capability, as well as its diesel potential.

Missing from the presentations in Detroit, however, was mention of the company’s hydrogen fuel-cell work—even in Tom Stephens’ (GM Group Vice President of GM Powertrain) introductory remarks about GM’s quest to “reinvent the automobile and to remove our vehicles from the environmental debate.” The current-generation Sequel fuel cell concept, announced last year at the Detroit show (earlier post), was absent from the floor.



It'll be interesting to see what the real world mileage of the Green Line Vue is. The Ford Escape Hybrid (best mileage hybrid SUV) is getting about 30 MPG for real world average mileage (http://www.greenhybrid.com/compare/mileage/). So if GM could come close to matching it that would be a good thing for GM.

I have to laugh at GM putting all that money for a full Hybrid System into a Big Truck - I'm sure those big pickup owners will all over that (wanting to pay alot more for better mileage via a hybrid system on a pickup). They should have gone with their original plan to put the full hybrid system in the Vue (instead of the cheap half attempt) - that's where the customers for a hybrid are.


I have to laugh at GM putting all that money for a full Hybrid System into a Big Truck - I'm sure those big pickup owners will all over that (wanting to pay alot more for better mileage via a hybrid system on a pickup). They should have gone with their original plan to put the full hybrid system in the Vue (instead of the cheap half attempt) - that's where the customers for a hybrid are.

I disagree with you here. There are two kinds of people who use trucks -- those who need them for the job they are doing, and those who want them regardless of their operational costs.

The first group may jump all over the improved mpg, because it lowers long term cost. The second group may jump all over the improved mpg, because it lowers long term cost.

GM's angle is that a 25% improvement in mpg is such a substantial savings in fuel precisely because these vehicles consume so much to begin with. Therefore, the amount saved (25% of the gas bill) is enough to more than pay for the hybrid upgrades.

I suspect that the GM play of improving MPG on its least efficient vehicles will pay off quite nicely, since 25% of the fuel bill for a V8 pickup is much larger than 25% of the fuel bill of a sedan. Furthermore, they can then lean on the government to require government purchasing of hybrid service vehicles for government agencies, thereby generating their own market that isn't competing (much) with Toyota or Honda.


Instead of diesel potential I think they should go exponential on diesel hybrids. With the big motor starter in them cold weather starting would be a breeze.


Applying hybrid technology to the vehicles which use the most fuel will definitely save more money on fuel. But, installing a hybrid system that will move a 3 ton tahoe is definitely going to cost more than one that is only required to move a 1.5ton sedan. The Tahoe above is going to have TWO 60kW motors, and enough batteries to drive them. The current Prius has a 30kW motor. I'm pretty sure that the price of the hybrid system will scale with its output.


Thats because gm is using a system they developed for a BUS and thus they are progressively downsizing it.


Maybe I'm not hip to the times or something but instead of driving a 6000 behemoth to pick the groceries and take the kids to school, why not just buy a smaller car? Yeah hybrid systems are great and all but national ad campaign that depicted the SUV driver as public enemy number one (think anti drug, anti drunk driving, anti smoking campaigns) would be far more effective at reducing fuel consumption and pollution than 50k hybrid SUVs. The people that buy these things are rich and very image conscious. The fact that they drive a hybrid SUV would just give them more ammunition to justify driving around in a tank. Do we really need to make this kind of behavior politically correct?


Many suvs get fairly good gas milage and hybrid ones get rather good milage. Dont forget a ton of people only have room for 2 cars and one of them is the long commute car so the other has to do everything else. Only a midsized/full sized suv can handle family touring grocery shopping by monthly /long haul family vacation trips with company.

Now that fewer people want to travel by jet a 1500 mile vacation trip to grandmas for xmas is not out of the question. And you sure as hell dont do that in a prius.


It seems that alot of you miss the point. What should be could be, does not matter. (people should buy smaller sedans instead of trucks.) People never do what we feel they should. Or trucks would not be such big sellers. Toyota and Honda both are jumping into the truck market. Why profit! I agree whole heartedly that gaining 25% in fuel economy is the right move to make on trucks. Pay back will be much faster. You wait and see Toyota and Honda will be jumping on board with their gas guzziling trucks!


Last year we learned that 250k out of the 1 million people that buy these thing every year don't really "need" the vehicles when gas went up by $1.30. Seems like we could take care of the rest of with a public ad campaign. I'm willing to bet that SUVs are less addictive than cigarettes.
Lets not forget that even if large SUVs had the same fuel economy of small cars, they still pose a threat to the health and safety of every other road user out there.


I disagree with reguard to where the hybrid customers are. I think the Tahoe was a bad choice, but there is a strong (and as yet, unfilled) demand for hybids work vehicles. My company spends nearly $5000/month in fuel in our service vehicles, if we could cut that by even 10% the savings would be worth it; especially since the initial vehicle purchase is tax deductable anyway.

I'd like to see GM put this 2-mode hybrid system into thier Express van next year; I'd buy 2.


This is terrific. I finally feel like an American car company can compete with the foreign makes again. I haven't felt this way, ever. If GM really pulls this two mode hybrid system off, it could be the turning point in American made transportation we've all been hoping for. I drive a small, foreign car, but I would actually consider trading *up* to an SUV that get's the same mileage, and is E85 compatible to boot. E85 is made from corn and the ethanol in it doesn't add to the carbon cycle, thus no added carbon to the atmosphere. It would make more sense to drive that than my non-E85, 30+ mpg Honda. It sounds like GM put a lot of thought into this, finally. This move is a message from GM that they can compete in the world and give people what they really want, finally.

This is just the beginning for GM. The trickle down effect will be a natural progression, as it is itself a trickle down of their bus technology. If they can get super high tech, and start integrating 21st century technologies into everything and making them much lighter but keeping the same relative size, they will adapt to the future needs of the survival of everyone. It's good to play a part in keeping your customers alive.

I'm against government advertising campaigns. The government has no business telling people how to live. If they want to regulate SUVs, just stop subsising them and make drivers pay their real costs. We still have relatively cheap gas compared to most. These folks should pay higher road taxes (SUVs are heavier and should pay a higher tax based on the damage they do to roads), charge a flat 10 cents a pound per year for any car and watch what happens. If they're truly more dangerous, the insurance companies have probably already taken that into consideration.


Do you need a family of Eight to test drive your Tahoe Hybrid , We are the real Brady Bunch. Would be glad to take the new Tahoe Hybrid to the extreme.



I can't wait for one! I drove a 1996 Tahoe for 200,000 miles and loved it. I then bought a crossover to downsize for efficiency & I hate it (Pontiac Aztec).
I want to be environmentally responsible, but I need the durability and room that an SUV provides.
Now I just have to decide if I will get the Vue while I'm waiting for the Tahoe to get into the used market (because contrary to popular belief, I'm not rich).

Paul Plant

I am viewing this page precisely because I am looking for an energy efficient, environmentally sensitive family and trailer hauler. I am convinced that a vehicle based on an electrical motor is the way to go, because it eliminates gas consumption at stop lights. Further, as battery technology improves, and becomes less expensive, these vehicles could be upgraded to provide longer electric only operation. Lets stop criticizing big vehicle owners who want to get good fuel economy and save the environment. There is a place and need for large vehicles. Lets get behind technology that makes it efficient and environmentally lower impact. If I could buy one large vehicle and carry 6 people at 27 to 30 mpg, or three Smart cars and get a combined fuel economy of 20 mpg, now what is smarter? Please make mine an AWD passenger G-Van with this two mode hybrid technology.


Hear, hear.
Big families need fuel savings too! Drop a hybrid system into a 12 passenger van for me.

I didn't buy my E150 because I like the way it handles....
I bought it because I have more family than a minivan can fit.

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