200kN MR damper was developed as a variable damper using two kinds of MR fluid. One is commercial product, and another is trial product. The experimental tests were conducted by excitation of sinusoidal wave, triangle wave, and random wave. As the result, the expected damping force was generated, and the basic characteristic of the damper was observed. In the domain of 0.15 [cm/s] to 20 [cm/s], force and piston velocity are in a proportional relation mostly, the fluid of trial product was understood that the ratio of force to piston velocity is larger and the width of the change to electric current is also larger compared with commercial fluid. When the period for the growth of the damper force by electric current was measured, it turns out that it has sufficient reaction speed.
