Prediction of traction indicators of wheeled tractors under dynamic nature of hooking strain
The main sources of the uneven impact of soil background on the work of machine-tractor unit is the unevenness of the surface of the soil background and the heterogeneity of soil inclusions in it, impermanence of hooking strain in time or traveled distance. The first group of causes forms the additional resistance to rolling of the tractor, the second group of reasons is a source of constant redistribution of vertical loads on tractor axles, generating its longitudinal angular vibrations. This random nature of loading and the spectrum of the generated effects from the soil background, with different phase displacements relative to each other may provide a continuous decline in bearing capacity of soil, leading to the variation of the coefficient of slipping of the tractor by separate curves of slipping. A deterministic analysis of the phenomena arising from the interaction of wheels with the soil in the described conditions allowed to develop a mathematical model for predicting the traction indicators of wheeled tractors of different design schemes, that takes into account the constructive parameters of the tractor, the geometric characteristics of the tire of the drive wheel, physico-mechanical properties of soil background, as well as the frequency and the amplitude of the hooking strain. Other factors, such as the inertial and elastic properties of the elements of power transmission, the possibility of self-generation of stable oscillations of the effective forces in the contact patch due to the periodicity of the change of tire grousers were considered in the model as constant in existing loading conditions. The calculation for this model, ultimately, allowed us to obtain static and dynamic curve of slipping of the tractor with the wheel formula 4x2. In general, theoretical evaluation of high-speed traction methods proved the necessity to take into account the reduced traction of agricultural tractors with increasing degree of uneven load on the hook.