Numerical Simulation of the Dynamic Behaviour of Tractors

摘要

From the very beginning of numerical ride dynamics simulation of agricultural tractors, mainly two fields of problems proved to complicate reliable predictions concerning the vehicle behaviour. First of all, this is the definition of useful terms to describe and quantify the often quite abstract aims of optimization, i.e. "ride safety" and "ride comfort". From a number of experimental investigations it is known that measured values and the driver's subjective feeling sometimes differ remarkably. For the numerical simulation this still means that a compromise has to be made between the actually intended renunciation of prototypes and an in-time pre-assessment by man, before a project stage with perhaps irreversible decisions for the vehicle concept might be reached. The nearly unquantifiable human perception especially of "ride comfort" and the resulting definition of corresponding terms for ist description call for a critical awareness when interpreting simulation results, but in fact they are not a problem of simulation. A much bigger problem is posed by the still unsatisfactory exactness of the predicted simulation results, which - in connection with the so far indisputable success of tractor simulation - may be surprising. But it has to be taken into account that in the past mostly tendencial statements were made concerning the effect of different optimization approaches and that they were accepted by the vehicle manufacturers as an important assistance. It was by comprehensive investigations on the effect of vehicle and cabin suspensions as well as absorber systems that the principal disadvantages of the standard tractor were uncovered and a process of rethinking of the manufacturers was provoked. The growing acceptance of TRAC vehicles as well as the presentation of corresponding concept studies is an unmistakable sign that this formerly very conservative market slowly started to move.