Detc 2001 / Dac - 21079 Analytical Target Cascading in Automotive Vehicle

Target cascading in product development is a systematic effort to propagate the desired top-level system design targets to appropriate specifications for subsystems and components in a consistent and efficient manner. If analysis models are available to represent the relevant design decisions, analytical target cascading can be formalized as a hierarchical multilevel optimization problem. The article demonstrates this complex modeling and solution process in the chassis design of a sport-utility vehicle. Ride quality and handling targets are cascaded down to systems and subsystems utilizing suspension, tire, and spring analysis models. Potential incompatibilities among targets and constraints throughout the entire system can be uncovered and the trade-offs involved in achieving system targets under different design scenarios can be quantified. NOMENCLATURE CDf tire lateral cornering stiffnesses for front CDr tire lateral cornering stiffnesses for rear Ksf stiffness of front suspensions Ksr stiffness of rear suspensions Ktf stiffness of front tires Ktr stiffness of rear tires Pif front tire inflation pressure Pir rear tire inflation pressure Po original design optimization problem Pv vehicle level target cascading optimization problem Ps system level target cascading optimization problem Pss subsystem level target cascading optimization problem RL target values of R from a lower level RU target values of R from an upper level R responses computed by analysis models T design targets 1 a distance from vehicle center of mass to front axle b distance from vehicle center of mass to rear axle f objective for the design problem g inequality constraints for the design problem h equality constraints for the design problem kus understeer gradient r response function u vehicle forward velocity x vector of all design variables ( , y) local design variables xmin lower bound of x xmax upper bound of x y linking design variables yL target values of y from a lower level yU target values of y from an upper level R target deviation tolerance for responses y target deviation tolerance for linking variables pitch natural frequency first natural frequency of front suspension first natural frequency of rear suspension second natural frequency (wheel hop frequency) of front suspension second natural frequency (wheel hop frequency) of rear suspension zsmax suspension deflection at jounce bumper contact