1994-03-01

Simulation and Evaluation of Semi-Active Suspensions 940864

A simulation of the vertical response of a nonlinear 1/4 car model consisting of a sprung and an unsprung mass was developed. It is being used for preliminary evaluation of various suspension configurations and control algorithms. Nonlinearities include hysteretic shock damping and switchable damping characteristics. Road inputs include discrete events such as bumps and potholes as well as randomly irregular roads having specified power spectral densities (PSDs).
Fast Fourier transform data analysis procedures are used to process data from the simulation to obtain PSDs, rms values, and histograms of various response quantities. To aid in assessing ride comfort, the 1/3 octave band rms acceleration of the sprung mass is calculated and compared with specifications suggested by the International Standards Organization (ISO). Cross plots of the rms values of acceleration, suspension travel, and the force of the road on the tire are used to compare the performance of various suspensions. These systems include semi-active systems with either on/off or continuously variable damping, passive systems, and an ideal skyhook system. These and other post processing procedures together with associated plotting capabilities are integrated with the simulation.
Example suspensions are compared to illustrate how the designer can utilize a number of ways to evaluate the performance of candidate designs. In so doing, the designer can obtain an increased physical “feel” for the system and use this increased knowledge to more rapidly develop new systems.

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