In this paper, a simplified 1-DOF vehicle suspension system with a semi-active on-off type damper was tesed and the possibilities of improving ride comfort were studied. It is known that the hydraulic damping, which present the damping force as proportional to the square of relative velocity, is more adequate to represent conventional fluid resisting type damper. The established governing equations adopted hydraulic damping and were solved and optimized as minimizing the object function which was defined as the summation of the acceleration and the relative displacements. The superiority of the so called semi-active type damper over the conventional passive type damping system was tested both in theoretically and experimentally. The results show that the semi-active damper is better than the constant damping coefficient passive type as simply comparing the values of the established object function.
