Narrow-Track Agricultural Tractors: A Survey on the Load of the Hand-Operated Foldable Rollbar.
To protect the driver in case of a tractor overturn, narrow-track tractors (used in vineyards and orchards) can be equipped with a rollover protective structure (ROPS) consisting of a two-pillar front-mounted foldable rollbar. The transition from the horizontal (rest) to the vertical (protection) position of this ROPS is performed manually by the driver. In addition to the time spent performing this task many times each day, a moderate physical load is required, given that these rollbars often have a mass of some tens of kilograms. In practice, neglect and poor attention to safety lead to the foldable rollbar remaining continuously in the rest position rather than being moved to the vertical (protection) position. Several rollover accidents have been fatal for the driver because the tractor, although equipped with a two-pillar front-mounted ROPS, had the rollbar in the horizontal position at the time of the event, thus assuring no protection to the driver. This issue is quite serious. To remove at least one of the problems for the proper management of this type of ROPS, the OECD has recently updated its Code 6 by introducing an optional test addressing the manual handling of front-mounted rollbars, providing a maximum load of 100 N. Several tests were conducted on new rollbars to ascertain the accuracy of this limit. The 100 N value was generally exceeded, which is cause for criticism. Indeed, a more appropriate reference for manual handling in this case would be the higher loads (up to 250 N) already provided by other standards for non-continuous tasks.
Foldable rollover protective structures: Universal lift-assist design.
The numbers of agricultural tractor rollover fatalities occurring with foldable rollover protective structures (FROPS) in their lowered position are significant. Raising and lowering the FROPS is a time consuming and strenuous process, and operators often leave the FROPS in the folded-down position providing no protection during a rollover. The purpose of this project is to design, manufacture, and test a lift-assist mechanism to raise and lower the FROPS from the operator's seat. The lift-assist design is based on the FROPS actuation forces, FROPS and tractor dimensions, and ergonomics engineering standards [SAE J898/ISO 6682 and SAE J1814]. The design considered can be retrofitted and will not modify or compromise the FROPS structure. A universal lift-assist lever design has been constructed and successfully tested for three FROPS of different sizes meeting appropriate ergonomics engineering standards. The operator actuation forces were less than the 75 N allowable maximum, and within the zones of comfort and reach for the operator. The lift-assist design uses an energy absorbing torsional spring to accommodate heavier FROPS designs.
Assessing Rollover Safety Provided by ROPS Tests Following SAE Standard J1194 versus OECD Code 4
OECD test codes were developed on the basis that the energy to be absorbed by the ROPS during an overturn is proportional to the tractor mass. The selection of the tractor mass used as a reference for the calculation of this energy determines the result of the tests. SAE Standard J2194 and the OECD codes/ISO standards/EU directives generally use the unballasted mass of tractors, but SAE Standard J1194 uses the maximum gross machine mass. We used 300 tractor models to compare the safety provided by the two different methodologies for testing ROPS: OECD Code 4 and SAE J1194. It was possible to establish that SAE J1194 provides a higher level of safety than Code 4 for tractors having ballast greater than 35% of their unballasted mass. SAE J1194 is more demanding with light tractors than with heavy tractors and, as the tractor mass in the moment of overturning can be very different from its unladen mass, it is more in line with the current situation of modern tractors. OECD Code 4 provides the same safety level for light and heavy tractors, but the level of real safety depends on the quotient between the maximum admissible and unballasted masses. Because of that, OECD Code 4 is valid for tractors having moderate ballast, but for highly ballasted tractors its validity is very doubtful.