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294 Multibody Systems Approach to Vehicle Dynamics
modelling the vehicle is actually ‘floating’ along under the action of these
forces at each corner. For a handling model the forces and moment at
the tyre to road contact patch which are usually calculated by the tyre
model are:
(a) F x – longitudinal tractive or braking force
(b) F y – lateral cornering force
(c) F z – vertical normal force
(d) M z – aligning moment
The other two moments which occur at the patch, M x the overturning
moment and M y the rolling resistance moment, are generally not significant
for a handling tyre model for passenger cars. The calculation of these
forces and moments at the contact patch is the essence of a tyre model and
will be discussed in more detail later.
As a simulation progresses and the equations for the vehicle and tyre are
solved at each solution point in time there is a flow of information between
the vehicle model and the tyre model. The tyre model must continually
receive information about the position, orientation and velocity at each
wheel centre and also the topography of the road surface in order to calculate
the forces and moment at the contact patch. The road surface is usually
flat but may well have changing frictional characteristics to represent varying
surface textures or changes between dry, wet or ice conditions. Inclined
or cambered road surfaces can also be modelled if needed. The information
Tyre model
F x
F y
Tyre model
M z
F z
F x
F y
M z
F z
Fig. 5.51 Interaction between vehicle model and tyre model. (This material has
been reproduced from the Proceedings of the Institution of Mechanical Engineers,
K1 Vol. 214 ‘The modelling and simulation of vehicle handling. Part 3: tyre
modelling’, M.V. Blundell, page 5, by permission of the Council of the Institution
of Mechanical Engineers)