EFFECTS OF TYRE INFLATION PRESSURE AND SURFACE CONDITIONS ON THE VIBRATION CHARACTERISTICS OF AGRICULTURAL TRACTORS

摘要

Spring stiffness and its damping coefficient of six agricultural tyres were measured by drop test using an indigenously developed drop test device. Experiments were conducted on three surface conditions, concrete, soil and asphalt with ten inflation pressures. Tyre inflation pressure and surface condition significantly influenced tyre spring stiffness and its damping coefficient values. The influence of tyre inflation pressure and surface condition on the vibration characteristics of agricultural tractor under different operating conditions, viz. standard rougher track (ISO5008), soil and asphalt surface, was evaluated. Vibrations were measured in three orthogonal axes; vertical, longitudinal and lateral at tractor base, seat base and on seat of agricultural tractor. A 25 HP tractor with five inflation pressures, three forward speeds and three operating conditions were the parameters studied. Methods for evaluating vibrations in relation to human health were referred from International Standard ISO 2631-1:1985, Mechanical Vibration and Shock - Evaluation of Human Exposure to Whole Body Vibration. Whole body vibrations (WBV) in longitudinal and lateral directions were not affected by tyre inflation pressure. On the other hand, tyre inflation pressure significantly influenced the level of WBV in vertical axis. In addition, the level of WBV for the three orthogonal axes was significantly influenced by tractor forward speed. Most vibration values at operator seat, suggested the potential risk on operator health, was occurred on standard rougher track followed by field operation, soil surface, and asphalt surface. However, it can be reduced by reducing tyre inflation pressure or tractor forward speed.