The aim of this paper is to construct a characteristic mathematical model of a selective hydro-pneumatic suspension system as well as harvesting energy of oscillation in a hydro-pneumatic accumulator placed onto a shock absorbing cylinder. The experimental test-bed of actual car suspensions and simulation model is performed on a quarter car model. The damping rates are studied and tested for different kinds of terrains experimentally and mathematically by very valuable advanced numerical simulation models. Further on, the paper performs an analysis and investigation for different kinds of control algorithms in order to select the optimal damping rate. System identification model is created using frequency domain identification techniques by transfer function model toolbox in Matlab Simulink. Fractional order system analysis, identification and fractional PID controller design, tuning and optimization in the context of the toolbox are presented. A program is constructed by Labview software to perform online simulation for the system. The program takes account of fluid mechanics, friction and nonlinearities of various sub-elements.