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Modelling and assembly of the full vehicle 337
trajectory and orientation as it moves vertically between full bump and
rebound positions. Scapaticci and Minen (1992) describe this approach as
the implementation of synthetic wheel trajectories. Such a method has been
adopted within MSC.ADAMS where the model is referred to as a ‘Concept
Suspension’ and is the basis of many dedicated vehicle dynamics modelling
software tools such as Milliken Research Associate’s VDMS, MSC’s
CarSim, University of Michigan’s ArcSim, and Leeds University’s VDAS.
The way in which such a model is applied is summarized in Figure 6.11. In
essence the vehicle model containing the concept suspension can be used to
investigate the suspension design parameters that can contribute to the
delivery of the desired vehicle handling characteristics without modelling of
the suspension linkages. In this way, the analyst can gain a clear understanding
of the dominant issues affecting some aspect of vehicle dynamics
performance. A case study is given in section 6.14 describing the use of a
reduced (3 degree of freedom) linear model to assess the influence of suspension
characteristics on straight-line stability. These models belong very
firmly in the ‘analysis’ segment of the overall process diagram described in
Chapter 1, Figure 1.6.
The functional representation of the model is based on components that
describe effects due to kinematics dependent on suspension geometry and
also elastic effects due to compliance within the suspension system. A
schematic to support an explanation of the function of this model is provided
in Figure 6.12.
∆v
∆γ
X
Z
∆z
Y
∆x
Fxt
∆δ
Fig. 6.12
Fy
Mz
∆y
Fxb
Wheel
trajectory
Concept Suspension system model schematic