CONCEPT AND DESIGN OF THE ROPS FOR A SMALL ARTICULATED TRACTOR FOR EXTREME SLOPED VINEYARDS

A new reversible wheeled articulated tractor has been designed and realized by WM s.r.l. (Prato all’Isarco, BZ, Italy) in collaboration with UNIBZ and FIR, to address the problem of working in terraced vineyards trained with the so-called “pergola” system, very common in mountain areas. The whole design process of this tractor was characterized by a constant dialogue between engineers and a selected pool of farmers, representative of final users, to have a product as much as possible answering to the users’ needs and, hence, free from future requests of design changes, according to the logic of Concurrent Engineering. In particular, conceiving and designing a ROPS suitable to equip this small tractor was a real engineering challenge: many design constraints, coming from the difficult environment in which this tractor will operate and resulting from the very particular design of the front part of the tractor, had to be matched with the (dimensional, structural) requests stated from the OECD code 7 used for homologation. The operating environment for this tractor imposed reduced dimensions to the external outline of this vehicle: vineyards inter-rows are very narrow (often lower than 1.00 m), as well as spans under the arbours (commonly ≤1.80 m, often 1.60 m). A high compactness of the vehicle was obtained by adopting an unconventional architecture for this tractor, i.e. an articulated body with a Diesel engine placed in the front part, a reversible driving seat directly placed on the motor, and the rear part acting as implement-carrier. Also the ROPS has some peculiarities, studied to match safety-volume requirements with the possibility for farmers of further reducing the overall height, if needed in some very narrow passages. In fact, the tractor was equipped with a non-removable, foldable and telescopic rear-mounted ROPS combined with a top horizontal element and a frontal protection for the driver’s feet. The absence of a conventional steering wheel (the tractor is driven by a cloche) and of an engine-bonnet in front of the driver make this ROPS absolutely unique and not-provided for by the norm; this latter fact puts two important questions to the testers, respectively on: (1) how defining the front part of the clearance zone (i.e. the point “D” of OECD code 7, fig.7.1.a p.23), usually defined in relation with the forward external edge steering wheel, and (2) how identifying the points of the tractor capable of supporting the whole mass of the upturned vehicle (i.e. the points defining the imaginary ground plane). Thanks to a careful interpretation of the inspiring principles of the norm and to the great experience of the UNIBO staff, these problems were successfully overcome respectively by (1) limiting the clearance zone to the vertical passing through the point “C” (OECD code 7, fig.7.1.a p.23), thus operating even with a higher safety level, and (2) by using the external edge of the feet protective structure to define the clearance zone and the virtual ground plane in case of upturning.