Development of a geometric slip flat model when turning a vehicle with two steering axles

Abstract

Introduction (problem statement and relevance). One of the main stages in the design ofspecial purpose vehicles is the calculation of the steering control. At that, engineers are guided by anumber of regulatory documents that lack one of the most important requirements, which is to minimize tire lateral deviation. The author notes the lack of scientific research in the field of geometric slip, which is caused by the non-compliance between the actual angles of wheels rotation and the calculated values for pure rolling and is an inherent property of any traditional steering linkage.The purpose of the study was to develop a mathematical model of the steering drive of a special-purpose vehicle with two steering axles to assess the geometric and power slip.Methodology and research methods. There is a known method for calculating the steering drive using trigonometric expressions, in particular the cosine theorem. The author proposed to use the coordinateiterative method developed by him and based on the equation of the sphere, with the steering wheel rotation angle in the kinematic calculation of the steering drive as a differentiation step. The choice of the steering drive parameters according to the conditions of symmetry and minimization of slip was carried out by the method of multivariable optimization.Results. In the course of the research, it was found that the choice of the characteristic of geometric noncompliance was a multi-parameter task, and changing one parameter led to the necessity of adjusting the others. If it was not possible to achieve zero geometric slip for all steered wheels, the task of optimizing the steering drive parameters wasreduced to minimizing geometric or total slip. The value of the slip essentially depended on the selected differentiation step. When choosing the characteristic of geometric slip, it was necessary to observe the condition of the steering linkage symmetry when turning left and right. When the wheels were turned from the neutral position to the periphery, the power and geometric slip compensated each other, which led to the decrease of the total slip and tire wear.The scientific novelty of the work lies in the development of a geometric slip model for a vehicle with two steerable axles, including a spatial model of the steering drive which allows to evaluate the influence of the geometric slip on the turn kinematics, as well as the mutual influence of geometric and power slip in order to select the steering drive optimal parameters of the multi-axle vehicle from the viewpoint of minimizing tire wear during curvilinear motion.Practical significance. The research results must be taken into account in the development of steering drive and turning control systems for multi-axle special-purpose vehicles, including them in the educational process as well.