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Modelling and assembly of the full vehicle 335 6.4.4 Swing arm model This model is developed from the equivalent roll stiffness mass model by using revolute joints to allow the suspensions for all four wheels to ‘swing’ relative to the vehicle body rather than using the suspensions linked on an axle. The revolute joints are located at the instant centres of the actual suspension linkage assembly. These positions are found by modelling the suspensions separately as described in Chapter 4. The swing arm model has an advantage over the roll centre model in that it allows the wheels to change camber angle independently of each other and relative to the vehicle body. The swing arm model is shown schematically in Figure 6.9. Although in the sketch the swing arms are shown with an axis parallel to the vehicle axis this need not be so in general. Also, although in the sketch the swing arms are shown as a ‘plausible’ mechanical arrangement (i.e. not overlapping) this also need not be so; in general contact between elements is not modelled for vehicle dynamics studies and in general the instant centres are widely spaced and not necessarily within the physical confines of the vehicle body. The swing arm model has the advantage over the equivalent roll stiffness model in that the heave and pitch ride behaviour can be included. 6.4.5 Linkage model The model based on linkages as shown in Figure 6.10 is the model that most closely represents the actual vehicle. This sort of vehicle model is the Fig. 6.10 Linkage model ‘as is’ approach

336 Multibody Systems Approach to Vehicle Dynamics most common approach adopted by MSC.ADAMS users in the automotive industry often extending the model definition to include full non-linear bush characteristics. A simplification of a model based on linkages is to treat the joints as rigid and generate a kinematic representation of the suspension system. As described in Chapter 4 a double wishbone arrangement is typical of a suspension system that can be modelled in this way and used for handling simulations (Pilling, 1995). 6.4.6 The concept suspension approach In addition to the four suspension modelling approaches just described another form of suspension model simplification (Scapaticci and Minen, 1992) considers an approach where the model contains no elements representing a physical connection between the road wheel and the chassis. Instead the movement of the road wheel with respect to the chassis is described by a functional representation, which describes the wheel centre Start with desired vehicle characteristics Trailing arm Double wishbone McPherson strut Using a concept suspension system find desired suspension characteristics Run optimization in MSC.ADAMS Select suspension type Suspension with desired characteristics Fig. 6.11 Application of a Concept Suspension model (provided courtesy of MSC.Software)

336 Multibody Systems Approach to Vehicle Dynamics<br />

most common approach adopted by MSC.ADAMS users in the automotive<br />

industry often extending the model definition to include full non-linear<br />

bush characteristics.<br />

A simplification of a model based on linkages is to treat the joints as rigid<br />

and generate a kinematic representation of the suspension system. As<br />

described in Chapter 4 a double wishbone arrangement is typical of a suspension<br />

system that can be modelled in this way and used for handling simulations<br />

(Pilling, 1995).<br />

6.4.6 The concept suspension approach<br />

In addition to the four suspension modelling approaches just described<br />

another form of suspension model simplification (Scapaticci and Minen,<br />

1992) considers an approach where the model contains no elements representing<br />

a physical connection between the road wheel and the chassis.<br />

Instead the movement of the road wheel with respect to the chassis is<br />

described by a functional representation, which describes the wheel centre<br />

Start with<br />

desired vehicle<br />

characteristics<br />

Trailing<br />

arm<br />

Double<br />

wishbone<br />

McPherson<br />

strut<br />

Using a concept<br />

suspension<br />

system find desired<br />

suspension<br />

characteristics<br />

Run optimization<br />

in MSC.ADAMS<br />

Select<br />

suspension type<br />

Suspension with<br />

desired<br />

characteristics<br />

Fig. 6.11 Application of a Concept Suspension model (provided courtesy of<br />

MSC.Software)

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