Page 467 - Automotive Engineering Powertrain Chassis System and Vehicle Body

15.1
Chapter 15.1

Modelling and assembly

of the full vehicle

Michael Blundell and Damian Harty

15.1.1 Introduction predictions of the vehicle response for typical proving
ground manoeuvres can be obtained.
The treatment that follows in this chapter will discuss
In this chapter we will address the main systems that
must be modelled and assembled to create and simulate a range of options that addresses the representation
the dynamics of the full vehicle system. The term ‘full of the suspension in the full vehicle as either an
vehicle system’ needs to be understood within the assembly of linkages or using simpler ‘conceptual’
context of this textbook. The use of powerful modern models. It is necessary here to start with the discussion
multibody systems software allows the modelling and of suspension representation in the full vehicle to set
simulation of a range of vehicle subsystems representing the scene for following sections dealing with the mod-
the chassis, engine, driveline and body areas of the elling of springs in simple suspension models or
vehicle. This is illustrated in Fig. 15.1-1 where it can be the derivation of roll stiffness. A case study provided at
seen that multibody systems models for each of these the end of this chapter will compare the simulated out-
areas are integrated to provide a detailed ‘literal’ puts for a simulated vehicle manoeuvre using a range of
representation of the full vehicle. Note that Fig. 15.1-1 suspension modelling strategies that are described in
includes the modelling of the driver and road as ele- Section 15.1.4.
ments of what is considered to constitute a full vehicle
system model.
In this chapter we restrict our discussion of ‘full ve- 15.1.2 The vehicle body
hicle system’ modelling to a level appropriate for the
simulation of the vehicle dynamics. As such the model- For the vehicle dynamics task the mass, centre of mass
ling of the suspension systems, anti-roll bars, steering position and mass moments of inertia of the vehicle body
system, steering inputs, brake system and drive inputs require definition within the multibody data set de-
to the road wheels will all be covered. With regard to scribing the full vehicle. It is important to note that the
steering the modelling of the driver inputs will also be body mass data may include not only the structural mass
described with a range of driver models. of the body-in-white but also the mass of the engine,
Note at this stage we do not consider the active ele- exhaust system, fuel tank, vehicle interior, driver, pas-
ments of vehicle control other than to introduce the sengers and any other payload. A modern CAD system,
modelling of ABS for vehicle braking. or the pre-processing capability, for example, in
For the vehicle dynamics task a starting point involving ADAMS/View, can combine all these components to
models of less elaborate construction than that suggested provide the analyst with a single lumped mass.
in Fig. 15.1-1 will provide useful insights much earlier Figure 15.1-2 shows a detailed representation of a full
in the design process. Provided such models correctly vehicle model. In a model such as this there are a number
distribute load to each tyre and involve a usefully accu- of methods that might be used to represent the individual
rate tyre model, such as the ‘Magic Formula’, good components. Using a model that most closely resembles
The Multibody Systems Approach to Vehicle Dynamics; ISBN: 9780750651127
Copyright Ó 2004 Michael Blundell and Damian Harty. All rights of reproduction, in any form, reserved.