Effects of rubber tracks on narrow-track tractors on the non-continuous rolling prediction model

Tractor rollover is one of the most hazardous events for the driver. The rollover protective structure (ROPS) was introduced to passively protect the driver. In the specific case of two-post protective structures fitted in front of the driver on narrow-track wheeled agricultural tractors, the ROPS has to avoid non-continuous rolling in the event of a lateral rollover. In order to check non-continuous rolling behavior in narrow-track wheeled agricultural tractors, a mathematical model is included in the preliminary ROPS tests of the standardized testing procedures issued by the Organization for Economic Cooperation and Development (OECD). A recent approach in the design of narrow-track tractors is the fitting of rubber tracks. A safety issue consequent to this new arrangement is that the standardized calculation does not cover narrow rubber-tracked tractors because it was originally developed assuming only the behavior of the tire in a lateral rollover. The aim of this study was to extend the field of application of the standardized calculation for non-continuous rolling behavior, allowing rubber-tracked tractors to be fitted with a front ROPS suitable for operation in narrow orchards and vineyards. The effect of track-ground interaction compared to tire-ground interaction was evaluated. The track shape and nondeformed behavior of the rubber track at a state of unstable equilibrium under full load caused the tractor to rotate around the outer edge of the track; therefore, the tipping axes and wheel characteristics in the original mathematical model were revised. The tracked tractor checked with the revised model required a higher ROPS with respect to the equivalent wheeled tractor to obtain non-rolling behavior. The ROPS needed to be increased by 0.28 m to meet the safety requirement.