Study on the Instability in a Loaded Hydraulic Servo-Mechanism : 1st Report, Effects of Compressibility of Oil and Sustained Oscillations

Abstract

In this report, instability to hydraulic servosystem with a piston-type control valve is studied.The investigation is carried out mainly on the system with underlapped valve. The effects of compressibility of oil on the system instability is examined, and then sustained oscillations caused by the compressibility are analyzed theoretically and experimentally. The results obtained are summarized as follows : 1. The system is completely stable under the assumption of incompressible oil flow, regardless of constant-pressure or constant-flow operation. And no sustained oscillation occurs in the system. 2. Compressibility of oil often makes the system unstable, and also sustained oscillations can occur. 3. The stability criteria of the system and some characteristics of sustained oscillations, both of which are derived by theoretical analysis, are compared with the results obtained from computations by analog computer and experiments. Their agreement is good.