Abstract
This paper details the mathematical modeling of a quarter car active suspension. An emphasis is placed on the hydraulic modeling and influence of hydraulic system dynamics on the behaviour of a vehicle active suspension. The servovalve equations are nonlinear equations whose flow rate outputs are functions of electrical current and a square root of pressure drop across the servovalve ports. By using linearization technique, the nonlinear equations were transformed to the linear ones. This allows that the complete transfer function linking between a quarter car and hydraulic models can be developed. Analytical bode plots and system pole plots are shown that the hydraulic component model is crucial to formulate accurate active control schemes.