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334 Multibody Systems Approach to Vehicle Dynamics
Note that this model shows the historical background to much of the current
unclear thinking about roll centres and their influence on vehicle
behaviour. With beam axles, as were prevalent in the 1920s, this model is a
good equivalent for looking at handling behaviour on flat surfaces and
ignoring ride inputs. For independent suspensions where the anti-roll geometry
remains relatively consistent with respect to the vehicle and where the
roll centres are relatively low (i.e. less than around 100 mm for a typical passenger
car) – a fairly typical double wishbone setup, for example – then this
approximation can be useful despite its systematic inaccuracy. However,
drawing general conclusions from such specific circumstances can be dangerous;
vehicles which combine a strut suspension at one end (with very
mobile anti-roll geometry) and double wishbone at the other (with relatively
constant anti-roll geometry) may not be amenable to such simplifications.
With this and all other simplified models, the analyst must consider
whether or not the conclusions that are drawn reflect upon the simplification
adopted or actually reveal some useful insight. The case study presented at
the end of the chapter shows a vehicle that behaves acceptably when modelled
in this way.
Spring
damper
Spring
damper
Rear right
swing arm
Spring
damper
REV
REV
REV
Rear left
swing arm
REV
Spring
damper
REV
REV
Front right
swing arm
and wheel knuckle
Front left
swing arm
and wheel knuckle
Fig. 6.9
Swing arm model approach