Page 300 - Understanding Automotive Electronics

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VEHICLE MOTION CONTROL 8

Figure 8.18
Tire Force Variation

FPO

With respect to the four frequency regions of Figure 8.18, the following
generally desired suspension damping characteristics can be identified.

Region Frequency (Hz) Damping

1: Sprung mass mode 1–2 High
2: Intermediate ride 2–8 Low
3: Unsprung mass resonance 8–20 High
4: Harshness > 20 Low

Another major input to the vehicle that affects handling is steering input
that causes maneuvers parallel to the road surface (e.g., cornering). Whenever
the car is executing such maneuvers, there is a lateral acceleration. This
acceleration acting through the center of gravity causes the vehicle to roll in a
direction opposite to the maneuver.
Car handling generally improves if the amount of roll for any given
maneuver is reduced. The rolling rate for a given car and maneuver is improved
if spring rate and shock absorber damping are increased. Although the
semiactive control system regulates only the damping, handling is improved by
increasing this damping as lateral acceleration increases.

UNDERSTANDING AUTOMOTIVE ELECTRONICS 287