Browse Publications Technical Papers 2004-01-3535
2004-11-30

Derivation of the Three-Dimensional Installation Ratio for Dual A-Arm Suspensions 2004-01-3535

Conventional suspension analysis of three-dimensional suspensions typically use two-dimensional analyses. This is done by projecting suspension components onto two-dimensional planes and then performing a two-dimensional analysis in each of these orthogonal planes or neglecting motions in one of the planes entirely. This requires multiple iterations because changes in one plane require a checking of their effects on motion in the other orthogonal planes. In doing so, much of the insight and accuracy gained from a three-dimensional analysis can be lost.
A three-dimensional kinematic analysis approach is presented and applied to a dual A-Arm suspension system. All motions are considered instantaneously about a screw axis instead of a point as used by the usual two-dimensional modeling approach. The model predicts deflections of suspension components in response to the three-dimensional forces present at the contact patch.
From this analysis, a three-dimensional installation ratio is generated using A-Arm mounting locations and A-Arm geometry. A wheel rate is then presented that includes the three-dimensional installation ratio, spring orientation, and spring rate. An example is included to compare the results of this 3-D approach to another popular suspension analysis computation tool.
Because the analysis is fully three dimensional, it can easily be adopted to calculate camber, caster, tire scrub, and other effects. Though equations are not derived for these here, some sample plots are included for the example suspension to show the capability of the approach.

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