Abstract
The tests that are normally proposed to characterize the stability of an agricultural machine are substantially of two types: (1) static tests of lateral overturning of a vehicle in a straight-ahead configuration, (2) static tests of lateral overturning of a vehicle in a specific steering configuration. These tests have as output the maximum angle of lateral overturning of a vehicle, measured when all the vehicle’s tanks are completely filled with their operating liquids and some weights are placed on the seat, to simulate the presence of the driver. There is also a third category of tests, less used, carried out via a system oscillating like a pendulum; the output of this test is the distance of the tractor’s centre-of-gravity (COG) from the oscillation point, and, thus, the vertical position of the COG. All these tests suffer from evident limitations, hereinafter briefly explained, and stimulate us to conceive a completely-new test apparatus that can overcome these shortcomings. Limiting the attention to the conditions of static stability only, the above-presented tests do not allow providing the complete spatial position (in Cartesian coordinates) of the COG in relation to the vehicle’s supporting base and, therefore, they prevent the prediction of the stability conditions of that vehicle when it travels on variously-inclined slopes and at angles with the maximum-slope direction different from the test conditions. Hence we design a first new- concept device, the tilting turntable, having the following characteristics: (1) the turntable has a circular shape and it is divided into quadrants capable of measuring the weight sustained by each of them due to the motionless vehicle positioned on them; (2) the turntable is installed on a tilting structure, and therefore it is able to simulate different gradients of the ground on which the vehicle is placed; (3) the turntable can rotate around an axis perpendicular to the surface supporting the vehicle, thus allowing to vary the angular position of the vehicle’s longitudinal axis with respect to the maximum-slope direction of the tiltable structure. This equipment will allow precisely locating the COG of a vehicle and making many experimental (static) tests simulating a lot of working conditions of agricultural machines on slopes. Moreover, common stability tests do not take in any way into account the load-transfer phenomena related to the velocity factor, concerning not only the appearance of a centrifugal force applied on the COG, but also a readjustment of the machine’s trim due to all the components having a certain elasticity (tires, suspensions where present, supports of the cabin) or having a degree of freedom in the plane transversal to the machine’s longitudinal axis (suspended loads, liquids, inconsistent solids such as grain products, stacked solids such as pseudo-spherical fruits). The behaviour of a mobile system of this type, having a dynamically-variable trim, could be difficult to predict a priori by only knowing the position of the COG inquired under static conditions. For these reasons, we propose a second system that allows to investigate experimentally also these dynamic aspects by reproducing any real-scale manoeuvres in a controlled and safe environment. The proposed system is a tiltable plane with dimensions (about 15 x 15 m) allowing an agricultural vehicle to travel on it along complete circular paths.
By integrating the tilting turntable and the tiltable plane, a new innovative test rig has been created: the tiltable platform. It will be installed within the “Agroforestry Innovation Laboratory” of the Free University of Bozen- Bolzano, located at the upcoming “NOI - Technology Park”.
