Analysis and Synthesis of Spool Valves With Arbitrary Metering Area Variation

Abstract

This paper presents a systematic method for analyzing and designing the notches on the spool of a flow control valve to influence the area-schedule, i.e., relationship between the spool position and the metering area. The motivation for such a flow control valve comes from a novel hydraulic actuator intended for camless valve actuation in internal combustion engines. The proposed actuator has a unique hydromechanical internal feedback system in which the motion of the flow regulator's spool is directly coupled to the motion of the actuator. Lack of direct control of the spool position necessitates the appropriate modification of the spool design in order to control the variation of the effective area across the valve. The design modifications required to realize the desired area-schedules are first discussed. A systematic procedure which combines computational fluid dynamics (CFD) analysis and geometry based analysis is then developed to characterize the variation of the effective area for various spool designs. It is shown that the mean area available for the fluid flow through the entire notch serves as a better approximation of the metering characteristics when compared to the traditional approach of using the minimum area. The proposed analysis procedure is validated with experimental data from a prototype spool valve. The fast turn around time of the proposed analysis technique is then used to develop an automated procedure to design the 3D features (notches) on the spool required to realize any specified area-schedule.