Calculation of nominal values of the main indicators of agricultural tractor

Abstract

As optimal values of the main indicators of tractor (energy intensity, power, operating weight, traction force, working speed) their nominal values are taken. Their calculation is a critical task of tractor theory. The aim of the study is to determine the nominal values of main indicators of tractor for maximum of propulsive coefficient and minimum of energy consumption. The objects of research are a wheel tractor with front steering wheels of smaller diameter than the rear ones and a caterpillar tractor. The main research method is calculation using computer programs with change of indicators by dichotomy method with given step in cycle. Low value of nominal energy intensity is determined by minimizing the function of specific power consumption that is the relationship of energy consumption during cultivating of a unit of area to a unit of performance and a unit of working speed. Low nominal values of power, operating weight, traction force and working speed are determined by the low value of nominal energy intensity, maximum propulsive coefficient and minimum energy consumption corresponding to tractor operation with permissible slipping. To determine the high values of nominal energy intensity a generalized non-dimensional coefficient of tractor efficiency is used, that is geometric mean values of partial non-dimensional coefficients of tractor efficiency on the operating weight, propulsive coefficient, fuel consumption per unit of area, performance, fuel consumption per unit of performance. With increasing of energy intensity the performance of tractor increases, but its efficiency on other indicators reduces. As upper limit of nominal energy intensity, a value is taken in which the reduction of generalized coefficient of tractor efficiency does not exceed 5%. At that the performance increases on 11-19%. Using the adopted optimality criteria, the intervals of changing of the nominal energy intensity of tractors are determined: 15,69-20 W/kg for wheeled tractors; 18,63-26 W/kg for caterpillar ones. For these intervals the nominal values of power, operating weight and working speed of wheeled and caterpillar tractors of 3-6 drawbar categories are determined.