4569846498

Simulation output and interpretation 415
K Tr
RC rear
Roll
axis
F ROy
F ROz
F RIy
h
A y
K Tf
F RIz
RC front
F FOy
F FIy
F FOz
F FIz
Fig. 7.19 Free-body diagram roll stiffness model during cornering
Consider next the components of force and moment acting on the vehicle
body in isolation.
Using the roll stiffness model as the basis for the analysis we are treating
the body as a single rigid axis with forces and moments transmitted from
the front and rear suspensions (axles) at points representing the front and
rear roll centres as shown in Figure 7.20. Consider the forces and moments
acting on the vehicle body rigid roll axis. Note that we are ignoring the
inclination of the roll axis. A roll moment (mA y h) acts about the axis and
is resisted in the model by the moments M FRC and M RRC resulting from the
front and rear roll stiffnesses K Tf and K Tr :
FFRCy FRRCy mAy 0
(7.17)
MFRC MRRC mAy h 0
(7.18)
The roll moment causes weight transfer between inner and outer wheels
(Figure 7.21). Taking moments for each of the front and rear axles shown
gives:
M
⎛ K
FRC
Tf
⎞
FFzM
may
h
t
⎜
f
KTf K
⎟ 1
⎝
Tr ⎠ tf
(7.19)
M
⎛ K ⎞
RRC
Tr
FRzM
may
h
t
⎜
r
KTf K
⎟ 1
⎝
Tr ⎠ tr
(7.20)
It can be seen from equations (7.19) and (7.20) that if the front roll stiffness
K Tf is greater than the rear roll stiffness K Tr there will be more weight transfer
at the front (and vice versa). It can also be seen that an increase in track