Metodologia para cálculo rápido das dimensões de pneus de tratores agrícolas

Abstract

RESUMO:Os primeiros tratores agrícolas utilizavam como elementos de locomoção rodas metálicas com garras. Diante da impossibilidade de circular por estradas, os danos provocados sobre os caminhos e o recalque em solo desagregado tornaram necessária a busca de outros materiais para os rodados dos tratores. Os rodados pneumáticos, ao se deformarem, adaptam-se melhor às irregularidades do terreno, aumentando a capacidade trativa e a comodidade para o operador. A diminuição da lastragem, substituída por cargas dinâmicas induzidas por transferência de peso, melhora ainda mais o desempenho das rodas no solo, convertendo-as em verdadeiros pontos de apoio. Apesar de toda evolução experimentada pelos rodados, os mesmo oferecem diversas opções técnicas que nem sempre são aproveitadas, pois nem todos os rodados disponíveis no mercado são apropriados para qualquer aplicação. O tamanho, as características técnicas, a pressão de inflação, etc. determinam o comportamento e a durabilidade. Assim, um rodado sobrecarregado tem pouca vida útil; por outro lado, o pensamento contrário onera o produto, uma vez que a falta de peso pode chegar a prejudicar sua função precípua, ressaltando-se que, ao não apoiar toda a banda de rodagem, pode-se aumentar a patinagem. Pelo exposto, torna necessário selecionar adequadamente o rodado para determinada aplicação e procurar que seu uso em cada momento, ocorra em condições que proporcionem melhores benefícios e maio durabilidade. PALAVRAS-CHAVE: pneus agrícolas; eficiência em tração, patinagem. METHODOLOGY FOR FAST CALCULATION OF AGRICULTURAL TRACTORS TIRES' DIMENSIONSABSTRACT: Primary agricultural tractors used metallic wheels with clutches as locomotion elements. Due to the impossibility to run in roads, damages provoked on the pathways and the suppression in disintegrated soil made necessary to seek other materials for the tractors' tread. The pneumatic tread, by being deformed, adjust better to irregularities on the ground, increasing the traction capacity and commodity for the operator. The decreased ballastage, replaced by dynamic loads induced by weight transference, improve even more the performance of the wheels in the soil, converting them in actual support points. In spite of the evolution experienced by the treads, they offer several technical options that aren't always used, because not every tread available in the market are appropriate for every application. The size, technical features, inflation pressure, etc. determine the behavior and durability. Thus, an overloaded tread has a decreased useful life; on the other hand, thinking otherwise charges the product, once the lack of weight can jeopardize its primary function, stressing that, by not supporting the whole tread, gliding can be increased. In consequence of the exposed above, it becomes necessary to choose the tread properly in order to determine the application and find out that its use for each moment occurs in conditions that provide better benefits and higher durability.

Evaluation of tractive performance of four agricultural tractors in laterally inclined terrain

“…According to the results presented in Table 2, the slippage of the right-side tires increased with increasing of the lateral inclination of the track to the tested tractors, except for the tractor T4, which obtained a minor slippage on the 25 degrees inclination on the tests of lateral track, which can be attributed to the greater weight transfer for the occurrence of the displacement of the center of gravity to the right side, due to increased lateral inclination of the track, according to KHOURY JUNIOR et al (2009). The T1 tractor was the only one whose slippage of the right-side tires was in the range of maximum tractive efficiency until the inclination of 10 degrees, according to MÁRQUES (2008), and 15 degrees forward, as ASABE (2006). The T3 tractor had the highest slippage on the inclination of 25 degrees, which can also be attributed to the fact the tractor is equipped with a larger rim tire and a narrow tread, as can be seen in Table 1.…”

“…According to MÁRQUES (2008), to achieve a traction efficiency of 0.93 on firm ground, the slippage should be between 4 and 8%. However, when the values of slippage grow the efficiency decreases significantly.…”