Page 54 - Understanding Automotive Electronics

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THE SYSTEMS APPROACH TO CONTROL AND INSTRUMENTATION 2

Figure 2.8
Frequency Response of an Example System

To illustrate this performance analysis method, consider the suspension
system, which is an important automotive system. Figure 2.9 is a simplified
representation of the suspension system at one wheel on a car. The car body
(sprung mass M ) is supported by a spring (depicted as K in Figure 2.9) and
s
shock absorber (denoted as D in Figure 2.9). The unsprung mass (wheel and
axle assembly) is displaced by force f, which is transmitted by the tire in
response to a rough road. The response of this system is the displacement x of
the unsprung mass relative to its rest position. The input to this system is a
force that in mathematical terms we denote F (t ).
Perhaps the most important input for characterizing system performance
is the sinusoid. In our example, we consider a sinusoidal force such as might

UNDERSTANDING AUTOMOTIVE ELECTRONICS 41