4569846498

Modelling and analysis of suspension systems 133
Table 4.1
Suspension design process activities
Wheel Body Handling Compliant Kinematic Component
load isolation load wheel wheel loading
variation control plane plane environment
control control
Investigate ✔ ✔ ✔ ✔ ✔ ✔
Set targets ✔ ✔ ✔ ✔ ✔ ✔
Verify ✔ ✔ ✔ ✔ ✔ ✔
systems, set design targets for components or to verify the performance of
proposed designs. Any rigorous design process must therefore be able to
quantify matters in these 18 different ways as shown in Table 4.1.
It is easy to focus on one small subset of the task above but to do so fails to
deliver the full range of benefits possible from multibody systems analysis
software. The software is generally expensive and the skilled personnel to
operate it are hard to come by and so such a focus represents a lost opportunity
for the organization.
4.1.1 Wheel load variation
Since a vehicle with four wheels is statically indeterminate with respect to
the calculation of reaction forces, only with some elastic behaviour (‘compliance’)
in the suspension can a determinate solution be formulated unless
some presumption of symmetry is made; otherwise, the ‘wobbly table’
case exists where there are at least three possible load distributions (Figure
4.2). This leads to abrupt fluctuations in load of a type barely tolerable in
restaurants and unconscionable for road vehicle behaviour. For the problem
shown we have one system and three possible reaction load solutions.
These include being balanced on the two longest legs (left in Figure 4.2) –
unlikely in practice but a solution in theory – or being balanced on three
Fig. 4.2
A classic case of static indeterminancy