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160 Multibody Systems Approach to Vehicle Dynamics
4.5 Suspension calculations
4.5.1 Measured outputs
A glossary of terms providing a formal specification of various suspension
characteristics has been provided by the Society of Automotive Engineers
(1976). In the past variations in formulations and terminology have been
provided by researchers, authors and also practising engineers following
corporate methodologies. The concept of a roll centre has also been subject
to a number of definitions (Dixon, 1987).
As discussed in Chapter 3 programs such as ADAMS/Car and ADAMS/
Chassis offer a range of pre-computed outputs for suspension characteristics.
The user documentation provided with those software systems includes
an extensive description of each output and need not be repeated here. For
completeness those outputs considered to be most common in their usage
and most relevant only to the following discussion in this textbook will be
described in this chapter.
As discussed in the previous sections, one of the main uses of a multibody
systems model of a suspension system is to establish during the design
process geometric position and orientation as a function of vertical movement
between the rebound and bump positions. As the output required does
not include dynamic response it is suitable to use a kinematic or quasistatic
analysis to simulate the motion. It should be noted that this information
could also be obtained using a CAD package or a program developed
solely for this purpose. The fact that a multibody systems program is used
is often associated with the stages of model development described in
Chapter 1 that lead through from the individual suspension model to a
model of the full vehicle.
A large number of parameters can be measured on an existing suspension
system and laboratory rigs such as the Kinematics and Compliance measurement
facility (or K&C Rig) described by Whitehead (1995) have been
developed specifically for this purpose. The descriptions provided here will
be limited to the most commonly calculated outputs, these being:
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Bump movement (spindle rise)
Wheel recession
Half track change
Steer (toe) angle
Camber angle
Castor angle
Steer axis inclination
Suspension trail
Ground level offset
Wheel rate
Roll centre height