Page 303 - Understanding Automotive Electronics

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8 VEHICLE MOTION CONTROL

Figure 8.21
Force versus
Relative Velocity of a
Solenoid-Switched
Aperture Shock
Absorber

FPO

each shock absorber. These actuators vary the oil passage orifice independently
at each wheel to obtain the desired damping for that wheel.
There are many possible control strategies and many of these are actually
used in production vehicles. For the purposes of this book, it is perhaps most
beneficial to present a representative control strategy that typifies features of a
number of actual production systems. We assume a solenoid-switched shock
absorber.
The important inputs to the vehicle suspension system come from road
roughness induced forces and inertial forces (due, for example, to cornering or
maneuvering), steering inputs, and vehicle speed. In our hypothetical simplified
control strategy these inputs are considered separately. When driving along a
nominally straight road with small steering inputs, the road input is dominant.
In this case, the control is based on the spectral content (frequency region) of
the relative motion. The controller (under program control) calculates the
spectrum of the relative velocity of the sprung and unsprung mass at each wheel

290 UNDERSTANDING AUTOMOTIVE ELECTRONICS