All Wheel Drive

All wheel drive systems were first introduced in the United states in 1983 in a rally-style racing coupe called the Quattro, by Audi. However, it wasn't until the late 1980's that all wheel drive became famous, through Subaru's 1800 series sedans and wagons. Due to the ingenuity of the system, all wheel drive soon became the standard for luxury midsize cars and SUVs. What made the all wheel drive system different was that only one differential is placed under the center of the vehicle instead of one at each end as is in four wheel drive. This new technology not only reduced weight and size, but also made the drive systems more effective in conditions where they are needed. The main feature of most modern all wheel drive systems is that when one wheel loses traction, the power is transferred to another, essentially eliminating the "one wheel wonder" effect of the previous systems where only one wheel would spin, whether it had traction or not.

The reason all wheel drive systems are not placed in all vehicles is because of the complexity of that center differential. The process of manufacturing and maintaining that mechanism is still rather costly, and the systems needed to support all wheel drive systems are costly as well. Typically an all wheel drive system has a central differential, which then evenly splits the engine's power between the front and rear differentials. Taking this into consideration, all wheel drive systems are almost always on full time. In order for all wheel drive to work, a specialized computer and a matching set of sensors is needed to tell which wheels are spinning and to which wheels the power should be transferred to. The change is done through a series of automatic wheel braking, adding another complicated and costly mechanism to the brakes system. For this reason all wheel drive systems were usually only used in vehicles like Mercedes and Porches. Lately, though, due to the advances in manufacturing technology, there have been a few domestic vehicles released, like the newer Ford Explorers and the Saab 9-2X, both of which feature all wheel drive. Should the cost of production of all wheel drive systems continue to decrease, more domestic vehicles will feature it in the future.

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Russell Gillmore 2004 F03