Manzone Marco

Trailers may increase the risk of tractor overturn during wood transportation in dangerous
conditions. In this work, tests were carried to simulate a trailer rollover using three two wheel
tractors and a crawler tractor and three trailers (two single-axle and one two-axle), all of their
combinations moving downhill along the path on a short dirt road. The trailers were always
loaded with the same load of logs cut at a length of about 1.5 m and put transversely to the
longitudinal axis of the trailer. During each test, the following parameters were measured: the
lateral dragging of the rear wheels/crawler of the tractor, the ground detachment of the rear
upstream wheel/crawler and both the longitudinal and transversal strains (released over the
tractor hooking system) produced by the trailer overturn. The study highlighted that the biaxle
trailer structure with a turntable steering had the best performances compared to the
single-axle in terms of safety during trailer overturning. Independently of the trailer type
considered in this work, a tied load is more dangerous than a load restrained only by steel
struts, because during the overturn the load forms a single unit with the trailer mass, which
increases the transversal and longitudinal strain.

Farm tractors are still widely used in many forestry operations. Predicting fuel and lubricant costs is difficult because their consumption depends on a number of factors such as hours worked and operations performed. Fuel and lubricant consumption is important since it can have an impact at both the economic and environmental level. Many fuel models have been studied in the last decades, but few studies have focused on oil consumption. The ASABE (American Society of Agricultural and Biological Engineers) Standard suggested a model for predicting engine oil consumption of farm tractors of the 1980s, which are potentially different from modern tractor engines. In addition, the recent widespread application of semi- and full-power-shift and continuous variable transmissions and the high number of hydraulic applications increased the amount of lubrication oil for transmission and hydraulic systems.

For these reasons, we analysed 133 4WD recent model farm tractors used in forest operations with the aim to study:

Þ   engine, transmission and hydraulic system oil capacities

Þ   engine oil change intervals as recommended by the manufacturers.

A new equation for engine oil consumption, as a function of the rated engine power, was first used and statistically analysed. It was similar to the equation developed by other authors (with a mean difference of 28%, decreasing to 11% at the highest engine power), but well below the ASABE model (with an average engine oil consumption three times higher). Another equation of total oil consumption related to the rated engine power was then studied and compared with a recent study. The results showed an average difference of 18%, decreasing to 8% at the highest engine power. The differences, due to a different machine dataset (only 4WD farm tractors that can be used for forestry operations were analysed) are, however, minimal also in the engine oil consumption model if compared with the oldest ones: a new proposal is therefore necessary, with new and affordable models for correctly evaluating economic and environmental forestry operation costs when using farm tractors.