抄録
Although hydraulic systems are compact and have high output power, there have been demands for further downsizing and higher output power in recent year. The operating pressure of hydraulic systems has been increasing, and thermal load and cavitation have occurred significantly as pressure has increased. Bubbles generated by cavitation remain submerged in hydraulic oil. The bubbles have a significant effect on bulk modulus because air is much more compressible than oil. The entrained air in the form of bubbles reduces the effective bulk modulus. Furthermore, air bubbles entrained in hydraulic fluids cause many problems in hydraulic systems. Active bubble elimination device using swirl flow capable of eliminating air bubbles from hydraulic fluid has been proposed and developed by our smart & clean hydraulic project. In this paper, we focus on the relation between the bulk modulus change and the bubble elimination from hydraulic fluid. Hydraulic fluid eliminated bubbles are sampled in a vessel and experimentally pressurized by a servo-piston. The volume and pressure change of the sampled oil is measured and bulk modulus change is calculated to evaluate the bubble elimination. We can conclude that the bulk modulus change of oil with bubble elimination affects system performance in relation to positioning, power loss, response time, and stability in hydraulic systems.
