Since the debut of the Honda Insight in 1999, hybrid has become a household word. Many new developments have occurred, and today the term hybrid encompasses mild, full, plug-in and two-mode variations. The similarity is each uses a combination of technologies to reduce fuel consumption. All hybrids in the United States are gas-electric hybrids, using a gasoline engine in concert with an electric motor or motors.

The functional difference between a mild and a full hybrid is the full hybrid can be driven on electric power alone, while the mild hybrid cannot. Mild hybrids have a combination starter/generator between the engine and transmission. It functions to keep the battery pack charged up via power from the engine. These vehicles will typically turn off the engine when coming to stop and then generate electricity from coasting. Then battery power is used to run accessories while stopped with the engine off and then to restart the engine automatically when needed.

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2008 Hybrids

Another technology that is incorporated is regenerative braking, which captures the normally wasted energy used to stop the vehicle with the brakes and uses it to recharge the battery. Currently, General Motors offers mild hybrids in the Chevrolet Malibu and Saturn Vue Green Line. They offer less of a fuel mileage advantage than a full hybrid, but also cost substantially less.

A full hybrid typically performs all of the above functions and also has an electric motor that can drive the wheels without using gasoline engine power. To save fuel, the electric motor can propel the vehicle at low speeds, such as when parking, traveling in stop-and-go traffic or when starting off from a complete stop until a certain speed is reached. The gas engine will turn on when that speed is attained – typically up to 25 mph depending on conditions – or when the batteries get run down.

Also, the electric motor can give an extra boost when accelerating, providing the vehicle more horsepower than it would have with the gasoline engine by itself. Since hybrid cars often have a smaller engine than their gasoline-only counterparts in the interest of better fuel economy, the extra power when needed means you don’t have to sacrifice as much performance.

Though automakers have been quick to point out that hybrids don’t have to – in fact, can’t – be plugged in, the “plug-in” hybrid is getting a lot of interest these days. When you start a full hybrid, the gasoline engine warms up, drives the car and charges the batteries before any hybrid functions occur. A plug-in hybrid is a full hybrid with a larger battery pack that you do plug in to recharge; that way, the first several miles of the day – perhaps an entire commute – are driven on electric power alone. Once that initial charge is used up, the vehicle works as a full hybrid.

At a recent Chicago area appearance, Bob Lutz, GM’s vice chairman of global product development, said the upcoming 2010 Chevrolet Volt often has been mistakenly called a plug-in hybrid by the media while it is actually an “extended-range electric vehicle.” The difference is that there is no mechanical connection between the gasoline engine and the wheels; the Volt is driven solely by an electric motor and the gas engine acts only as an on-board generator to recharge the batteries. If the batteries are plugged in and charged up, GM says the Volt will have a range of up to 40 miles of gasoline-free, zero-emissions driving before the gas engine is needed.

The new two-mode hybrid that GM developed with Chrysler and BMW consists of two electric motors and four fixed mechanical gears. What sets it apart is the electric motors can be completely bypassed, automatically of course, and you can have mechanical gas engine power straight through to the rear wheels when towing or hauling, or even just accelerating. Traditional hybrids always route engine power through the electric motor, and in situations of high demand, this actually reduces efficiency. It also requires larger electric motors. That’s why most full hybrids post better city than highway mileage. The two-mode hybrid can still drive a full-size truck up to 30 mph on pure electric power.

The two-mode hybrid system is contained in something about the size of the automatic transmission it replaces, plus the battery pack. The GMC Yukon and Chevy Tahoe Hybrids from GM, and Dodge Durango and Chrysler Aspen Hybrids from Chrysler are already on sale, albeit in limited numbers. GM is launching full-size pickup two-mode hybrids this fall as 2009 models, while the hybrid Dodge Ram isn’t due out until the 2010 model. Both Chrysler and GM use their cylinder deactivation features, multidisplacement system and active fuel management, respectively, to allow these V-8-powered hybrid trucks to run on four cylinders when possible for additional fuel savings.

A two-mode hybrid BMW X6 is in the works, as is a Saturn Vue Green Line 2 Mode Hybrid, which will be the first use of this technology in a front-wheel drive application.