Impacto da massa de um pulverizador montado sobre o equilíbrio operacional de um trator agrícola

Abstract

The agricultural tractor is the most complex and interesting piece of equipment for most of the activities permitted on a rural property. Each specific activity will require the power generated by the tractor in different ways, and it is necessary to adapt it to the activity to be performed. It is necessary to adjust the tractor's mass by adding or removing ballast on the axles and/or water in the tires and tire pressure, always extracting the maximum that the tractor can deliver within the safety limits and adequate conditions of the equipment. Implements coupled to the three point hitch with specific weight transfer specifications in relation to other types of hitch. This type of hitch allows the height of the implement to vary in relation to the ground by means of a hydraulic system. Therefore, the objective of this study was to evaluate the operational balance of an agricultural tractor as a function of the mass of an implement engaged in the three-point hydraulic system and specific characteristics of the tractor's tires. The relationships and effects between the mass of an implement coupled to the three-point hydraulic lift system and different internal tire pressures on the mass distribution between the tractor axles, tire contact area, kinematic advance and horizontal displacement of the center of gravity were presented. The experimental configuration consisted of the following factors: implement mass (1150, 850, 550 kg), tire pressure (151,685, 165,474, 179,264, 193,053 kPa). To evaluate the 12 treatments, a randomized block experimental design was used from the combination of the levels of the trained factors, resulting in a 3x4 factorial. Five replicates per treatment were performed for the variables, except for the tire contact area. The mass of the implement mounted on the tractor impacted the mass distribution on the axles, going from 60%-40% to approximately 90%-10%, generating an unsafe condition. Although tire pressure influences the advance, it must be adjusted according to the mass on the axles. Even complying with the ISO/TC 22 - Road vehicles standard, the distribution of mass between the axles can compromise the safety of the operator and the integrity of the assembly. The displaced center of gravity, which varied by approximately 21%, to the rear axle raises the front axle, directing the contact area of the front tires. With a lower implement mass, the contact area of the rear tires also decreases. The tractor's cinematic advance is affected by the mass due to the greater effort of the drive wheels and varies from 4 to 8%. Therefore, attention to the distribution of the assembly mass and tire pressure must be redoubled, as it directly affects the operating conditions.