|  The 2007 Saturn Vue Green Line Hybrid is the first GM vehicle powered by a new, more affordable hybrid system that delivers an estimated 20-percent improvement in fuel economy, depending on driving conditions. It is expected to deliver an EPA estimated 27 mpg in the city and the best highway mileage of any SUV at 32 mpg.
A unique powertrain is the key. A 170-hp, 2.4-liter, four-cylinder engine with variable valve timing is teamed with an electric motor-generator. Most hybrids use a continuously variable transmission, but not the Vue Green Line. Saturn stuck with its trusty 4T45-E four-speed automatic transmission to keep the price down.
To further improve fuel economy, the Vue has two driver-selectable operating modes. The economy mode improves fuel economy by minimizing the air conditioning's accessory drag on the engine.
The star of the Green Line's engineering show is the dual-purpose motor-generator—that big alternator. Hung off the side of the engine in plain view, it not only performs the function of an alternator, but performs like an electric motor, delivering torque back to the gasoline engine when the power is needed most. The gasoline engine produces 170 horsepower and 164 pound-feet of torque, with another 115 lb-ft of torque on call from the electric motor.
This solution is elegant in its simplicity, as it enables the balance of the powertrain to remain much closer to a standard non-hybrid unit, saving on engineering and manufacturing costs. Electric power for the power steering, climate control and other accessories is driven by a modest battery pack that fits unnoticed behind the rear seat under the cargo floor.
The Vue starts conventionally, with no unfamiliar noises or physical sensations. Under acceleration, the 4-speed automatic shifts smoothly. It's only when you lift off the accelerator pedal that you note something different. Most vehicles coast with only a vague sense of slowing — not the Green Line. If you're not on the accelerator, you're slowing down, a result of the Green Line's regenerative braking system that is busy converting kenitec energy into electricity stored for later use. Applying the brakes also takes some getting use to, as they grab quickly and take lots of practice to achieve a smooth chauffer's stop.
Like other hybrids, the gasoline engine shuts down when the Vue is at rest. It is a funny sensation to have the engine just stop, and it took days to fight the urge to restart the engine at each traffic light. The electric motor/generator comes into play most often when accelerating from a rest. As the driver's foot releases the brake pedal, the motor-generator spins the engine's crankshaft up to speed in order to assist the gasoline engine with a smooth launch from a stop. The motor is also capable of providing additional torque when maximum acceleration is called for. Unlike other current hybrids, however, the Green Line does not run any distance on pure electric power; the motor-generator is a hybrid "helper."
This model will replace the 2007 Vue sometime this summer with a Green Line version due in the fall of 2007. The newer model should prove to be a better performing vehicle, as it will use GM's new two-mode hybrid system that delivers a 45-percent gain in combined fuel economy verses the non-hybrid Vue model, GM says.
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