4569846498

194 Multibody Systems Approach to Vehicle Dynamics
While the approximate method produces usefully accurate results for this
simplified model, when a real suspension system is analysed in MSC.ADAMS
using the same method (eigenvalues predicted by the ADAMS/Linear
product) using the same data but including real wishbone and elastomer
geometry, the results can be seen to be somewhat different.
The first and most obvious source of error is the use of the spring rate
directly from the detailed model in the simplified 2 DOF models. In the literal
model, as in the real vehicle, the motion of the wheel does not directly
correspond to the motion of the spring. Using the model, the so-called
‘motion ratio’ can be examined between spring and wheel. It can be seen
(Figure 4.59) that the spring changes length by 1.43 mm for every 1 mm of
Figure 4.58 MSC.ADAMS prediction of the modes of vibration for the full
linkage quarter vehicle model with elastomers and individual component mass
and inertia data. Primary ride mode (top left) 0.95 Hz. Wheel hop mode (top
right) 10.78 Hz. Fore–aft compliance mode (bottom left) 17.35 Hz. Unsprung
mass lateral mode (bottom right) 47.31 Hz
305.0
case4
Spring length (mm)
295.0
285.0
275.0
265.0
255.0
245.0
235.0
225.0
215.0
SPRING_2324.Translational_Displacement.Z
205.0
100.0 50.0 0.0 50.0 100.0
Analysis: Last_Run
Wheel travel (mm)
2003-08-05 00:11:16
Fig. 4.59
Spring motion with respect to wheel motion from the model