Influence of Differential Locking on Tractor Work Rate: Part 2, Simulation of a Two-Wheel-Drive Tractor when Turning

In a previous paper, the authors have shown that the distribution of power between two driving wheels, by means of a controlled differential, does not improve the traction efficiency to such an extent that the use of this expensive mechanism is justified in two-wheel-drive (2WD) agricultural tractors. This conclusion was drawn from calculations made with a simulation program, where the tractor was assumed to travel in a straight path. To investigate if this conclusion is also valid when turning, a more elaborated simulation program for a two-axle vehicle has been devised. This modified simulation program takes into account the following features: the side forces developed when travelling in curves, the transverse load transfer which gives different traction capabilities to each driving wheel, the influence of tyre inflation pressure and wheel load on traction and the difference between the wheel radii used on the one hand to compute the driving moments (the moment arm) and on the other hand to calculate the travel speed (the rolling radius). When the tractor is turning, the model shows that the controlled differential gives the least reduction in tractive efficiency and therefore the highest work rate, but the possible improvement compared with an ideal standard differential is only of real importance when the turning radius is small (