STRUCTURAL MODIFICATION EFFECTS ON THE DYNAMIC BEHAVIOR OF AN AGRICULTURAL TRACTOR

Even during normal operation, agricultural machines are exposed to a number of disturbances that can generate excessive vibration levels. The disturbances originate from soil roughness in combination with driving speed or from rotating elements within the machine. Machine vibrations may be uncomfortable to the driver. Vibrations may affect the manual or automatic controls and reduce the efficiency of the operations to be carried out such as field spraying and tillage. In this article, the dynamic behavior of a tractor is studied and the effects of possible structural modifications on its dynamic behavior are examined. Using the experimental modal analysis technique, a modal model is derived (with a correlation coefficient ranging from 0.90 to 0.95 of the measured values) that contains the eigenfrequencies and mode shapes of the machine. It is applied to predict the structural behavior of the machine under a set of excitation conditions. A frequency sensitivity analysis on the modal model gives information about the most critical locations on the structure with respect to local parameter changes. In a later stage, this is used to predict frequency shifts owing to structural modifications like localstiffness and inertia changes.