Advanced Cost Functions for Evaluation of Lateral Vehicle Dynamics

Abstract

AbstractThe paper introduces the method of assessment of vehicle manoeuvres through a set of global cost functions. The corresponding cost functions can be derived for different domains like longitudinal and lateral dynamics, driving comfort and other. The procedures of the computation of the cost functions include in general: (1) Selection of vehicle dynamics parameters relevant to the domain; (2) Transformation the appointed parameter to the dimensionless form; (3) Definition of weighting factors for each of the appointed parameters with taking into account that the weighting factors can be variable depending on the type of the vehicle manoeuvre as well as on the driving conditions; (4) Calculation of the cost function for the selected domain; (5) Calculation of a global cost function in the case of the integrated assessment of the manoeuvre through several domains of the vehicle dynamics. The described procedures are discussed in the paper as applied to the domain of lateral vehicle dynamics. The parameters chosen for the calculation of the corresponding cost function are the lateral acceleration a y , the yaw rate dψ/dt, and the sideslip angle β. To transform these parameters to a dimensionless form, the procedure is proposed that uses the function of root mean square of deviations between reference and actual values for each variable. This procedure implements also an original method of definition of reference values for lateral acceleration a y and yaw rate dψ/dt. The method is based on the variation of understeer characteristic of the baseline vehicle with the aim to extend the linear region and to reduce the understeer gradient as well as to increase the maximum level of lateral acceleration. The validation of the developed methods and procedures is illustrated by way of model-in-the-loop simulation. The test programme covers several standard manoeuvres—steady-state circle, slalom and avoidance manoeuvre—performed for a simulator, medium-sized passenger car. The numerical values of the cost functions for each manoeuvre are introduced and analyzed. The further applications of the developed technique can be: (1) Assessment of vehicle dynamics based on criterions of performance and stability; (2) Optimization of vehicle dynamics control systems; (3) Choice of proper control strategies/tuning of control gains and resolution of critical control situations by simultaneous operation of several systems like ABS, TCS, TV/vehicle dynamics control.KeywordsVehicle dynamicsCost functionsStabilityWeighting factorsSimulation