Terrain mobility performance optimization: Fundamentals for autonomous vehicle applications Part II. Computational simulation, implementation for mobility design, and validation

Abstract

Based on an analysis of vehicle mobility performance indices in use, it is shown that an index for the optimization of autonomous vehicle mobility performance should be constituted as a set of technical parameters that should result directly from the interactive dynamics of tires and terrain and should be measurable and controllable in real-time. Besides, the combination of the parameters should characterize the vehicle’s technical productivity/efficiency (not energy efficiency), and thus, enable the estimation and control of vehicle mobility performance. If such requirements are satisfied, the index can be optimized and optimization results can facilitate autonomous control design. This article provides results of a study to address the above-formulated requirements in the proposed mobility performance index.Part II discusses the computational results of mobility performance optimization for a 4x4 vehicle simulated on three homogeneous terrains and split terrains on flat surface and on slopes, with and without drawbar pull. Additionally, the vehicle with three conventional driveline systems is simulated in the same terrain conditions, and a detailed analysis establishes dependences between the optimal tire slippages and optimal circumferential forces of the wheels and their correlation to those provided by the driveline systems. Advantages of the mobility optimization for control design are explained and discussed. It is also concluded that the use of energy efficiency indices in mobility performance assessment can be considered as a supplementary, but not the primary subject-heading of the vehicle mobility performance.The mobility performance optimization directly contributes to mobility design that is illustrated by conceptual implementation of the optimization results in two driveline systems of the 4x4 vehicle: a driveline with positive engagement of the power-dividing units and a virtual driveline that serves for fully electric vehicles with in-wheel motors.Finally, a verification of the mobility optimization results and validation of the proposed mobility performance index is conducted through statistics-based assessment against experimental wheel circumferential forces and tire slippages.