Road Vehicle Modeling Requirements for Optimization of Ride and Handling

Abstract

The design process of road vehicles, very often based on intuition and experience, can be greatly enhanced through the use of generalized optimization techniques. A methodology based on the use flexible multibody models for the ride and stability optimization of vehicles is proposed here. This procedure allows the use of complex shaped deformable bodies, represented by finite elements, while the gross rigid body motion is captured using co-rotational frames. Rigid bodies represent almost undeformable system components. The methodology proposed is exemplified through the application to a road vehicle with flexible chassis, described as a flexible multibody system. The vehicle optimum design is achieved through the use of an algorithm with finite differences sensitivities, included in a general-purpose package. The vehicle components characteristics are the design variables while constraints on their relative motion and limiting values are imposed. The major difference between the analysis models used for vehicle ride and for handling lies in the description of the tires and road. For comfort improvement the road model is profiled, i.e., it simply contains the information on its height for the left and right side of the wheel sets independently. No lateral forces are specified for the tire road interaction and the tire model only includes the radial deformations. The handling analysis of the vehicle dynamics requires that a three-dimensional description of the road is provided and that the tire model can handle lateral forces. The ride optimization is achieved by finding the optimum of a ride index that is the outcome of a metric that accounts for the acceleration measured in several key points of the vehicle, weighted according to its importance to the occupant comfort. Simulations with various vehicle speeds and different road profiles and geometries, accounting for diverse ride and handling conditions, are used to exemplify applications of the proposed methods.