Efficient simulation of a sports car in steady-state cornering.

Abstract

— The analysis and optimization of full nonlinear flexible multi-body models of race car ve hicles often requiere long execution times. Vehicle dynamics engineers demand for particular-purpose, simplified or reduced models, to get quick results without losing accuracy, as well as customized pre processing and post-processing tools for combining lap-time simulators, tire characteristics interpo lators, and suspension kinematic simulators, among others. In this work, a simplified vehicle model for a sports car including all the main nonlinearities required to compute the steady-state behavior in cornering is presented. This software complements lap-time simulators that can predict the optimal lap time for a track but cannot analyze the stability and robustness of the vehicle. Nonlinearities in cluded are present in the kinematics of the suspension and steering mechanisms, anti-roll bars, in the constitutive laws of springs, and in tire characteristics (including lateral slip, longitudinal slip, and in clination angles dependencies). The complete kinematic analysis of the suspension, including anti-roll bars, is previously computed off-line using suspension design software and finite elements-based soft ware. Each analysis is parameterized by the strut length of each quarter of the vehicle suspension and the rack travel of the steering system, thus all characteristic dimensions needed for force and moment computations in the equilibrium equations are stored in the form of double input tables (car database). These discrete values are linearly interpolated for non-stored values of the parameters. The nonlin ear kineto-static equilibrium equations for the vehicle in cornering configuration are solved in several nested stages using iterative Regula-Falsi methods for root finding of nonlinear equations. For a given vehicle setup and a given trim of the track, yaw moment diagrams and other characteristic curves could be obtained quickly, producing a readable map of controllability and robustness of the vehicle.