21
C H A P T E R 3
Stability of Untripped Vehicle
Rollover
To help mitigate the occurrence of rollover accidents at problem locations, rollover detection and
warning is necessary. At a minimum, problem locations may have speed reduction signs, rollover
warning signs, and chevrons to pre-warn all drivers of the potentially dangerous curve ahead.
Although signing is present at most problem locations, many drivers become desensitized to a
specific warning amongst the multitude of other roadside signs [22]. So, accurate and real-time
detection and warning of the impending danger of a vehicle rollover is important for improving
vehicle active safety and reduce the occurrence of rollover accidents. In this chapter, the roll
indexes and warning for untripped vehicle rollover is studied and analyzed.
3.1 ROLL INDEX OF UNTRIPPED VEHICLE ROLLOVER
is section introduces some typical rollover evaluation method which can predict untripped
vehicle rollover includes static stability factor, dynamics stability factor, and lateral load transfer
ratio.
3.1.1 STATIC STABILITY FACTOR
Many passive warning systems use a prediction algorithm to determine the threat of impending
rollover based on the values of vehicle roll angle and/or lateral acceleration. In order to help
measure the likelihood of vehicle rollover, a rollover resistance rating program was proposed
by NHTSA, which uses the Static Stability Factor (SSF) [4, 5, 23]. In SSF, the stiffness and
damping of suspension system and tires are ignored. Applying torque balance equation to one
side tires of the vehicle, the following equation can be derived:
ma
y
H mg sin
B
H C F
zi
T
w
1
2
mgT
w
; (3.1)
where
B
is road ramp angle, H represents the height of center of mass, measures upward from
the road, F
zi
is vertical force of the other side tires, and T
w
is the track width.
Assuming the road ramp angle is zero, when the vertical force on the other side tire of
vehicle is reduced to 0, being F
zi
D 0, it is believed that the vehicle will roll over. en the SSF
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