The power delivery efficiency of a mechanical front wheel drive tractor. A computational and experimental study

The reduction of fuel consumptions and the improvement of the efficiency of agricultural vehicles are themes that recently have attracted investments from the industrial and scientific community; in this context a study aimed to maximize the efficiency passing through the optimization of the constructive features of an agricultural tractor is certainly suitable. Many studies have been performed for generical off-road vehicles but for agricultural tractors there is still the need to deepen this topic. Agricultural tractors present a very unique powertrain, this means that for the vast majority of cases they are mechanical front wheel drive(M.F.W.D.) and non-isodiametric vehicles. A M.F.W.D. vehicle doesn't use any kind of central differential or transfer case but the engine torque is splitted between the front and rear axle using a pair of meshing gears. In this thesis the vehicle has been modeled following a bottom-up approach: starting from the wheel/soil interaction and arriving to the computation of the power delivery efficiency. The good correlation between simulations and experimental data ensures the reliability of the model. Subsequently five constructive parameters: mass distribution, wheels'radius ratio, wheelbase, drawbar height and front wheels'lead have been varied on eight levels, for each simulation the power delivery efficiency has been evaluated; afterwards a gradient method allowed the estimation of the three most influential parameters.These three parameters, have been used as indipendent variables of a reduced second order polynomial model. The first derivative of the reduced model,subsequently set equal to zero, provides the expression of the optimal mass distribution.The study conducted showed that the best configuration is an isodiametric vehicle with the mass distribution slightly shifted towards the front axle. Non isodiametric tractors have proved to be less efficient than the isodiametric ones and having the optimal mass distribution markedly shifted towards the rear axle.