4569846498

Modelling and assembly of the full vehicle 327
for each of these areas are integrated to provide a detailed ‘literal’ representation
of the full vehicle. Note that Figure 6.1 includes the modelling of the
driver and road as elements of what is considered to constitute a full vehicle
system model.
In this chapter we restrict our discussion of ‘full vehicle system’ modelling
to a level appropriate for the simulation of the vehicle dynamics. As such
the modelling of the suspension systems, anti-roll bars, steering system,
steering inputs, brake system and drive inputs to the road wheels will all be
covered. With regard to steering the modelling of the driver inputs will also
be described with a range of driver models.
Note at this stage we do not consider the active elements of vehicle control
other than to introduce the modelling of ABS for vehicle braking. Chapter
8 is dedicated to the modelling of active systems.
For the vehicle dynamics task a starting point involving models of less
elaborate construction than that suggested in Figure 6.1 will provide useful
insights much earlier in the design process. Provided such models
correctly distribute load to each tyre and involve a usefully accurate tyre
model, such as the ‘Magic Formula’ described in Chapter 5, good predictions
of the vehicle response for typical proving ground manoeuvres can
be obtained.
The modelling of the suspension system was considered in detail in
Chapter 4. The treatment that follows in this chapter will discuss a range
of options that addresses the representation of the suspension in the full
vehicle as either an assembly of linkages or using simpler ‘conceptual’
models. It is necessary here to start with the discussion of suspension
representation in the full vehicle to set the scene for following sections
dealing with the modelling of springs in simple suspension models or the
derivation of roll stiffness. A case study provided at the end of this chapter
will compare the simulated outputs for a simulated vehicle manoeuvre
using a range of suspension modelling strategies that are described in
Section 6.4.
6.2 The vehicle body
For the vehicle dynamics task the mass, centre of mass position and mass
moments of inertia of the vehicle body require definition within the multibody
data set describing the full vehicle. It is important to note that the body
mass data may include not only the structural mass of the body-in-white but
also the mass of the engine, exhaust system, fuel tank, vehicle interior,
driver, passengers and any other payload. A modern CAD system, or the
pre-processing capability, for example, in ADAMS/View, can combine all
these components to provide the analyst with a single lumped mass.
Figure 6.2 shows a detailed representation of a full vehicle model. In a model
such as this there are a number of methods that might be used to represent
the individual components. Using a model that most closely resembles the
actual vehicle, components such as the engine might, for example, be elastically
mounted on the vehicle body using bush elements to represent the
engine mounts.