This study evaluates and provides solutions to the problem
of poor subjective feel of seat suspensions that employ
magnetorheological (MR) dampers and skyhook control. An
Isringhausen seat suspension that had been modified to
replace the stock passive damper with a controllable MR
damper was used to evaluate the problems and potential
solutions. A seat suspension tester was built using materials
from 80/20 Incorporated and a hydraulic actuation system
from MTS. An HP Dynamic Signal Analyzer was used as the
main piece of data acquisition equipment, along with a
Pentium PC and National Instruments Data Acquisition card.
All of the hardware is installed in a controlled laboratory
facility at Virginia Tech's Advanced Vehicle Dynamics Lab.
The first task was to analyze the source of the unexpected
peak in the acceleration spectrum of the suspended seat.
This analysis was accomplished using a combination of pure
tone inputs and a Fourier analysis of a simple model of the
system. This analysis indicated that the peak is actually
three times the resonant frequency of the seat suspension.
The analysis also indicates that the frequency components
continue at odd multiples of the resonant frequency, however,
the third peak is the most noticeable. The third multiple
is in the resonant frequency range (4-8 Hz) of the human
body, so it was initially blamed for the poor subjective
feel of the seat. However, solutions to remove this harmonic
were tested without success.
The work progressed to a time domain analysis, which eventually
led to determining the source of the poor subjective feel.
The seat suspension was excited with a variety of inputs.
The seat acceleration and damper control current were examined
in the time domain to show that the cause of the poor subjective
feel is the control signal discontinuities. The control
policy was modified to remove the control signal discontinuities
and was found to improve the subjective feel of the seat.
Finally, several two-degree-of-freedom control policies were
implemented and tested. Although the results from this testing
are inconclusive, they generated several recommendations for
future research.
