## 5 Conclusions  
This study has focused on isolating harmful low-frequency vibrations that are transmitted to the vehicle's seat. The solution is based on lowering the natural frequency of the system by introducing an isolation system with low or zero dynamic stiffness, and thus, the frequency range of isolation will be increased.  
The practical implementation for the proposed vibration isolation system is based on implementing a simple and compact system that combines the merits of the QZS with an air spring, which is able to isolate extremely low levels of vibrations. Herein, the novelty of the proposed system is (i) its capability of isolating the unpredictable roadway low-level disturbances and (ii) its compatibility with B-segment and C-segment cars, which are considered important factors for the future of passenger car production.  
Parametric analyses were performed to prove the efficiency of the proposed system in terms of the displacement transmissibility (a pointer of efficiency). Displacement transmissibility was tested under different amplitudes of excitation, different driver loads, and different damping coefficients. For each test, a comparison was generated between the proposed system and an equivalent linear mass-spring-damper system. The results have revealed that the proposed system was very efficient and better than the equivalent linear system under all circumstances. It was also observed that the proposed system provides lower peak transmissibility and a broader range of frequency isolation. More specifically, the proposed system was able to isolate vibrations at very low frequencies of excitation down to 0.65 Hz. Thus, for different conditions of excitation amplitudes and driver loads, the range of frequency of isolation was still suitable at less than 1.85 Hz.  
Future research efforts will be dedicated to the implementation of the proposed system to perform experimental tests to verify the system performance compared with the simulation results. Finally, further studies are required to explore the effects of the air spring pressure, airflow, inflation, and deflation control for the isolator efficiency.  
Conceptualization, methodology, investigation, and original draft preparation: M.A. ([PERSON]), Y.D., L.H. and I.H.A.; review and editing: M.A. ([PERSON]), L.H., I.H.A.,Y.D. and M.A. ([PERSON]); supervision: P.P. and M.A. ([PERSON]); project administration and funding acquisition: P.P. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The authors would like to thank the Mechanical and Mechatronics Engineering Departments at An-Najah National University for providing access to their labs for executing data analysis. Sincere thanks are also extended to the University of Luxembourg for its continuous support.  
The authors declare no conflict of interest.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline Load (kg) & & 60 & 140 \\ \hline \multirow{2}{*}{Frequency (Hz)} & Proposed & 1.44 & 1.15 \\ \cline{2-4}  & Linear & 4.17 & 3.88 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Values for 0 dB frequencies at different loads.