1  Investigation of load assumptions

1.4 Obstacle avoidance

The stated observation of the onset of resonance during quick lane changes led to an investigation of an "obstacle avoidance" maneuver similar to lane changing in which the transverse distance is distinctly smaller, meaning that the achievable lane changing time may also be shorter. Since no observations under practical conditions were available, experienced truck drivers were asked whether it would be possible to change lanes in a loaded truck with a sideways offset of one meter within 1.5 seconds. The answers were in the affirmative, but the drivers‘ "gut feeling" was that this was a borderline maneuver.

Figure 6: Obstacle avoidance action of 1.0 m with a half-value period of 0.75 s

The results are in line with expectations. Figure 6 shows the evasive maneuver of 1 meter sideways with a half-value period of 0.75 seconds. The forces are shown normalized to acceleration values in the unit g. The transverse force on the cargo is distinctly out of phase with the centrifugal force with an oscillation offset of approx. p/2. This means that at least the first maximum of the transverse force, corresponding to 0.32 g, is made up solely of the downhill force and tangential forces, because the centrifugal force is equal to zero at that point. The second maximum is greater in absolute terms than the first and reaches 0.41 g. At this maximum too, the tangential acceleration from the rolling oscillation predominates. The rise from 0.32 g to 0.41 g is attributable to resonant excitation.

It may thus be concluded that while extremely short avoidance maneuvers similar to lane changing (objects on the roadway) do not necessarily cause transverse acceleration values of greater than 0.5 g, they may involve significant rolling acceleration components which must be taken into account inter alia for assessing the rolling factor.