Asymmetrical Lap and Other Non-Linearities in Valve-Controlled Hydraulic Actuators

Abstract

The results of a theoretical investigation into the effect of asymmetrical lap on the open-loop performance of valve-controlled hydraulic actuators are presented. The governing differential equations of the system are developed in a non-dimensional form. The effects of supply lap and exhaust lap on actuator peak pressures, ram amplitude and cavitation, as well as the effect of inertia load on actuator peak pressure and output amplitude, are shown. When the open-loop frequency response of the hydraulic servomechanism is attempted experimentally the ram drifts until it hits its stops. In previous theoretical analyses this effect has not been noted. This paper demonstrates that the inclusion of a term ignored in previous work highlights this effect. This same term is shown to give a kind of feedback when the system drives a vertical inertia load.