Study of the maximum estimate of vehicle’s net thrust coefficient
Theoretical dependencies are known, which allow estimating the cohesion force of the vehicle with the bearing surface. From the point of view of practical use, the results obtained are not convenient, since in order to obtain a numerical estimate of the force or the net thrust coefficient, it is necessary to integrate the function of shear stress from shear strain, which is variable along the length of the contact patch, which is a laborious computational problem. To clarify practical estimates of the cohesion of the mover to the soil, further research is needed, including the search for the maximum value of the shear stress integral, taking into account the variable slip ratio. This article is devoted to the solution of this computational problem. The study bases on the methods of the theory of off-the-road transport locomotion. When implementing theoretical models, information about the physical and mechanical properties of soils is used. The calculations were made in the Maple 2017 program using built-in high-level commands. The analysis of the calculated data and their approximation were performed by the least squares method (LSM) with an assessment of the significance of the coefficients of the approximating functions. As a result of the study, dependences were obtained that allow in practice to estimate the maximum value of the net thrust coefficient of the vehicle to the bearing surface and the corresponding slip ratio. The equations take into account the physical and mechanical properties of the soil (specific cohesion, the angle of internal friction and the shear modulus) and the vehicle parameters (the length of the contact patch, the average normal pressure over the contact patch, the grousers’ spacing). We believe that the use of the proposed formulae will make it possible to carry out a refined calculation of the tractive performance of wheeled and tracked forestry vehicles interacting with deformable forest soil.