Abstract
Abstract
An analysis of the tractive efficiency of four-wheel-drive vehicles is conducted from the perspective of maximizing efficiency of slip with respect to non-uniform traction conditions in particular. The analysis is conducted using a more rigorous mathematical analysis than previously and using a thorough graphical analysis to substantiate the mathematical analysis. Previous studies concluded that under all traction conditions efficiency of slip will be a maximum when the slip of each wheel is equal. The analysis revealed that, contrary to the previous literature, efficiency of slip will not be a maximum when the slip of each wheel is equal under non-uniform traction conditions. When applied to a vehicle with an interaxle fixed ratio coupling, this means that the optimum theoretical speed ratio is not always equal to 1. An example of non-uniform traction conditions is the situation where two drive wheels are on soil and the other two are on tarmac. The improvement in the efficiency of slip, in this example, when using the correct theoretical speed ratio (as opposed to that equal to 1) is particularly marked at high drawbar loads. The method by which the correct theoretical speed ratio is to be achieved when non-uniform traction conditions occur is problematic. The drive system would require a drive mechanism and a level of intelligence not currently found in off-road vehicles.
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