4569846498

440 Multibody Systems Approach to Vehicle Dynamics
Off
Throttle
influence
On
100
RWD
To understeer
50
0
To oversteer
50 100
Clutch down,
(Passive) handling
FWD
Typical performance 4WD
Fig. 7.39 Vehicle behaviour on-throttle – flaws or brand attributes? The
illustration is informal, the quantities of understeer and oversteer being some
undefined ‘%’
the oversteer departure – i.e. the loose behaviour at the limit – of rear-wheeldrive
vehicles (Figure 7.39). If smart systems on board disallow such a
departure, keeping the vehicle stubbornly linear until the end of the available
friction, will it surprise the driver when the friction is exceeded? Will
it bore the driver and tempt him or her to buy a different, less perfect brand
next time? Or will the retention of YRG as AyG falls off give a uniformly
better driving experience, less tainted by some of today’s compromises?
Certainly the use of signal-to-noise ratio can potentially address many
issues simultaneously:
● linearity of yaw rate gain with lateral acceleration
● delays in response degrading driver confidence
● roll/yaw interaction
● disturbance rejection
● throttle/steer interaction
– FWD – minimizing ‘push’ under power
– RWD – reducing oversteer departure tendency under power
– 4WD – minimizing ‘push’ under power
● brake/steer interaction
Of some importance for the successful application of the method is the balancing
of the proportion of different events in the overall signal-to-noise
calculation. For instance, when comparing the influence of crosswind disturbance
rejection with the influence of roll–yaw interaction, due account
must be taken of how many ‘crosswind’ events there are for every ‘aggressive
turn-in’ event and so on, lest one become unduly weighted in comparison
with others. It is likely that the selection of the sign-off cycle will be
what ultimately determines the dynamic brand attributes of the vehicle.
This is not so different to the current situation where vehicles are tuned to
match the preferences of key individuals at their preferred test facilities.
These differences are a source of richness and diversity in vehicle design and
are part of the larger commercial process of ‘differentiation’ to retain or
increase market share.