In this research, a semi active control system with continuous variations along with hydro active dampers and springs is developed for a passenger car. The improvement of dynamic behavior of a passenger car with regard to weight constraint, energy consumption and cost highlights the need for the employment of such a semi active suspension system. Here, a full car model with hydro active subsystems including roll, pitch, bounce movements, and one degree of freedom for the driver is extracted, unlike the previous research in which merely the bouncing motion has been taken into account. By using the linearized car model equipped with the proposed hydro active system, the optimal damping force based on full state feedback control and LQR method is obtained for the improvement of the ride comfort and stability. In addition, practical constraints on manufacturing of the components and delay in the control system are dealt with. The car is excited by a disturbance such as a bump imparted to the wheels for which the idea of the wheel based filtering was also considered. The simulation results in the time domain for the hydro active suspension system demonstrate significant improvements in all controlled modes in comparison with the passive system. On the other hand, in comparison with the fully active system, the proposed system has an additional advantage in terms of energy consumption and weight reduction in the required hardware.