Steering System Optimization of a Ford Heavy-Commercial Vehicle Using Kinematic & Compliance Analysis 2012-01-1937

The basic scope of heavy-commercial vehicle (HCV) development which was just concentrated on fuel-economy, durability and performance feel is not capable of fulfilling the increasing customer expectations anymore. HCV developers concentrate on additional vehicle attributes such as steering, ride comfort, NVH, braking, ergonomics and exterior-interior design in order to provide the passenger-car like perception to HCV drivers during long distance drives.

The objective of this paper is to present the model validation methodology and the optimization study on suspension & steering hard points of a HCV. The results of the optimization study on suspension kinematics and steering performance of the vehicle is verified using both full vehicle simulations and vehicle testing.

A full vehicle ADAMS/Car model is used for the validation and optimization study which has beam-element leaf springs on solid axle and air springs on drive axle for front and rear, respectively. The steering system of the mentioned HCV consists of a steering wheel, steering column subsystem, a variable-ratio steering gear with recirculating ball mechanism, a pitman arm, a drag link, an upper steering arm, two lower steering arms and a tie-rod. All steering linkages are modeled as rigid bodies in ADAMS/Car model during the optimization study. The optimization factors are selected as pitman arm-to-drag link hard point, drag link-to-upper steering arm hard point, and lower steering arm-to-tie rod hard point. The aim of this optimization study is to improve and find an optimum point for the kinematic properties such as bump steer, roll steer, percent Ackermann, maximum wheel angle and their symmetry. The improvements on kinematic properties are verified with vehicle testing on different maneuvers with the prototype vehicles.