Pressure Transients Generated during the Rapid Braking of Asymmetric Hydraulic Actuators

Abstract

This paper presents a theoretical and experimental study of the pressure variations that arise when a moving inertia load, driven by a hydraulic actuator, is braked by returning the closed-centre spool control valve to its mid-position. There are two predominant nonlinearities—the occurrence of cavitation in the hydraulic oil and the relationship between load position and hydraulic stiffness. A mathematical model is derived and solutions are obtained by three methods. The first is a digital simulation on a mini-computer, the second uses phase plane, and the third uses the techniques of small perturbations to linearize the problem. For typical values of the parameters, the linearized analysis is shown to yield results in good agreement with the computer solution. When the valve is moved rapidly from an open to a closed position, large pressure peaks and cavitation can occur. This has been verified experimentally with good agreement between predicted and observed pressure peaks. Thus the maximum pressure generated can be conservatively estimated using the straightforward linear expressions.