Limitations to suspension performance in a two-degree-of-freedom car active suspension

  • 1 Faculty of Information Technology –Czech Technical University in Prague, the Czech Republic


It is often assumed that if practical difficulties are neglected, active systems could produce in principle arbitrary ideal behavior. This paper presents the factorization approach that is taken to derive limitations of achievable frequency responses for active vehicle suspension systems in terms of invariant frequency points and restricted rate of decay at high frequencies. The factorization approach enables us to determine complete sets of such constraints on various transfer functions from the load and road disturbance inputs for typical choices of measured outputs and then choose the “most advantageous” vector of the measurements from the point of view of the widest class of the achievable frequency responses. Using a simple linear two degree-of-freedom car suspension system model it will be shown that even using complete state feedback and in the case of in which the system is controllable in the control theory sense, there still are limitations to suspension performance in the fully active state.



  1. Freudenberg, J. S., Looze, D. P., Right-half Plane Poles and Zeros and Design Tradeoffs in Feedback Systems, IEEE Transactions on Automatic Control, 30/6, 1985
  2. Hyniova, K., Frequency Response Limitations for Active Suspension of Vehicles, Micro-CAD 99 – International Computer Science Conference, Miskolc, pp. 209-217, 2006,
  3. Hyniova, K., Achievable Dynamic Responses for Active Suspension System of Vehicles, Habilitation thesis, Prague, 2000
  4. Zhou, K., Doyle, J.C., Essentials of Robust Control, Prentice Hall, London, 1998

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