Abstract
Although hydraulic systems have high-power and quick responsibility because its oil has high rigidity, when air bubbles are mixed into oil, they reduce the oil rigidity and change the dynamic characteristics; thus, air bubbles generally should be removed from hydraulic oil. In this study, however, we consider that the reduction of oil rigidity advantageously can works for absorbing impact, and propose to positively utilize the air compressibility for hydraulic actuator. The purpose of this study is to develop a new hydraulic actuator using the compressibility of air effectively. This paper proposes the structure of new hydraulic cylinder. This cylinder has two pistons, and mixed fluid chamber between the two pistons. In the mixed fluid chamber, the hydraulic oil containing air bubbles can be filled. The rigidity of the actuator can be adjusted by changing the amount of air bubbles in oil. To accurately adjust the rigidity of the hydraulic oil in the mixed fluid chamber, it is needed to understand the relationship between the air bubble content and the effective bulk modulus of the hydraulic oil. To clarify the relationship, we propose a mathematical model that expresses the relationship between pressure and effective bulk modulus of oil contains air bubbles. This paper also evaluates the validity of the mathematical model of the effective bulk modulus experimentally. The experiments are conducted by changing pressure in chamber filled with oil containing air bubbles. We confirm that the effective bulk modulus calculated using the mathematical model agrees well with the experimental results. Moreover, the displacement and pressure response of the new cylinder is analyzed by numerical simulation. The results show that air in the cylinder valid for increasing the performance of the impact absorption.
