PREDICTION AND EXPERIMENTAL VALIDATION OF THE FIELD TRACTIVE PERFORMANCE OF A RUBBER TRACK UNIT

Satisfactory analysis of the tractive performance parameters (rolling resistance, drawbar pull and tractive efficiency) of agricultural vehicles depends on accurate prediction of the forces between the soil and the wheels or tracks of the vehicle. These parameters are, in turn, determined by the normal and shear stresses at the wheel or track-to-soil interface. In order to predict these parameters accurately, the basic shape of wheel or track-to-soil interaction must be well understood. In this paper, a model using structural analysis technique and an iterative procedure which avoids the need of predetermining the shape of track-to-soil interaction has been successfully applied to predict the normal and shear forces at the interface. The path of each point, determined by the nodal coordinates of small flexible track segments between the road wheels, and the soil deformation at each point are fed into the model. The forces generated at each point on the interface are calculated by the conventional soil-vehicle mechanics techniques. These are then integrated to provide the overall force at the interface. Thus, the method applied to this problem takes account of the fact that the path of a point at the track-to-soil interface depends not only on slip and sinkage but also on the resilience of the track. Predicted tractive performance results obtained by this method were validated by comparing them with the experimental field data obtained using a single wheel tester. The general trend of the coefficient of traction was correctly predicted with absolute errors of about 6·5% (at 20% slip) as compared with the curve fitted to the experimental results. © 1994 Silsoe Research Institute.