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This paper describes a building block approach for understanding the past, present and future four wheel drive systems. The emphasis will be on light trucks and sport utility vehicles. It will describe the advantages of four wheel drive and how it improves performance and safety. The building block approach is a tool for categorizing the basic systems in the market. Systems are separated into main component areas and are rated for the effect they have on the overall performance and safety. This paper can be used as a means for understanding a very complex 4x4 market.

This paper will show the growth of the Global 4x4 market ( Figure 1), and define terms for 4x4, 4WD and AWD. This will allow a way to organize the data and show the growth trends of the AWD segment. This growth can be seen in Figure 2. From this point of view, the vehicle, and technology differences will be shown, both with physical pictures, and schematic architecture diagrams. The focus will be the US 4WD and AWD market from 1997 to 2004, when a significant change occurred from 4WD to AWD architectures. Figure 1 This paper will document the changes that have occurred to bring about the distinct shift towards AWD car based vehicles from truck based 4WD vehicles. It will be clear why the terms were defined as they were when the architectural differences are shown schematically. Figures 25, 26, 27 and 28.

This paper will show the trends in the 4 wheel drive vehicles, technologies, and the move to systems approach rather than the independent supplier approach. The trends show how the transfer case and other drive train components are changing using the latest technology. These changes are making more system adaptations possible. There are three directions that the current changes are moving into. 1) Continue to optimize current designs 2) Redesign with new devices and 3) Design new 4WD systems. Examples of future 4WD designs are Hybrid Electric Vehicles with motors at all four wheels, and CVT's. Specifically this paper will show the latest trends from 1994 to 1998 and some predictions into the future. The focus will be the U.S. Market but some references will be made to the world 4x4 market. Brief references will be made to the basics of traction and directional stability as they relate to the 4WD technology.

Traction Control Systems improve the general safety of a vehicle by providing better handling, directional stability and traction under various driving conditions. Consumers are becoming more aware of the benefits of traction control and the automobile manufacturers are responding with vehicles incorporating various kinds of traction control systems. This paper attempts to organize the various systems by the general principles used in their implementation and strategy. The basic elements of vehicle dynamics and the tire-patch mechanics are described. The influence of other subsystems like suspension and steering on vehicle dynamics is analyzed. The need for and the schemes used for the measurement of the various dynamic parameters are delineated. The advantages and limitations of the various control strategies are also described in relation to vehicle operating conditions.