INTRODUCTION In the automotive industry, customer clinics and owner surveys continually emphasize ride and handling performance as an important driver of purchase decisions and ownership satisfaction. Of the elements defining this performance, damper tuning is among the most important. Dampers having digressive force-velocity relationships have distinct vehicle performance advantages over linear and progressive dampers, emphasizing roll damping and low- to mid-speed motion control at reduced bump force levels. The velocity range of automotive suspension dampers is generally divided into three regions: low-, mid-, and high- speed, with a different hydraulic valve controlling each range in rebound and compression. With digressive deflected disc dampers, mid-speed control force around the “blow-off” transition point is determined by the pre-load which arises from the product of hub off-set and disc stack stiffness. To maintain mid-range control level, digressiveness is adjusted by simultaneously changing hub off-set and disc stack stiffness in opposite directions. Because this involves the development of a new complimentary disc stack, evaluation requires a laborious trial and error process. Shortened product development cycles preclude fullexploration of force digression if traditional methods are utilized. To address this need, a regression-based method has been developed that directly calculates new disc stack stiffness to compliment changes in hub offset, enabling efficient optimization of damper digressiveness. BACKGROUND Digressiveness Defined Figure 1. Digressive Force-Velocity Curves 2013-01-1357 Published 04/08/2013 Copyright © 2013 SAE International doi:10.4271/2013-01-1357 saepcmech.saejournals.org A Computational Method for Efficient Hub Offset Comparisons with Deflected-Disc Dampers W. Bradley Cwycyshyn and Joseph Fedullo General Motors Company ABSTRACT With deflected-disc dampers, digressive force-velocity shapes are achieved via the combined effects of disc stack stiffness and hub-offset. The degree of digressiveness can be adjusted to alter vehicle performance by changing the proportion of these parameters. Optimizing this relationship can yield substantial vehicle performance improvements, but the time consuming iterative process of developing a new disc stack for each hub-offset discourages experimentation. To enable more efficient digressiveness comparisons, a regression-based computational method has been developed which converts disc stack stiffness from one hub-offset to other offsets directly, without iteration. Once an initial disc stack for one offset has been tuned by traditional methods, stacks for other offsets can be calculated that maintain overall damper control. This paper will present background information on deflected disc valving and curve shaping, describe development of the computational method, and show an example of a typical comparison, graphically. CITATION: Cwycyshyn, W. and Fedullo, J., "A Computational Method for Efficient Hub Offset Comparisons with Deflected-Disc Dampers," SAE Int. J. Passeng. Cars - Mech. Syst. 6(3):2013, doi:10.4271/2013-01-1357. ____________________________________ 1383Downloaded from SAE International by Universiti Teknologi Malaysia, Sunday, April 12, 2015For the purposes of this paper, a digressive damper is defined as one with a marked reduction in slope of the force vs. velocity curve above the “blow-off” force. Examples of two levels of digressiveness are depicted in Figure 1. The Need for Digressiveness Digressiveness is driven by vehicle-level requirements; the forces required for optimum hydraulic control in the low- mid velocity range (roll damping, primary motion control), and the forces required for optimum control at higher velocities (bump force, wheel control, etc.) cannot be achieved simultaneously without a force modulating device. Without this device, forces build either progressively or linearly with velocity resulting in excessive forces a