Experiments indicate that at small servovalve spool displacements, leakage flow between the valve spool and body dominates the orifice flow through the valve. In precision positioning applications, where the servovalve operates within the null region, this flow, if ignored, may severely degrade the performance of a conventional servohydraulic design. We have developed an improved servovalve model that combines both leakage and orifice flow. The model was developed by reviewing experimental leakage flow data and identifying a simple mathematical form that (1) made physical sense and (2) replicated experimental data. When combined with orifice relations, the model extends the accuracy and region of applicability of existing servovalve models. Furthermore, the combined model is easily parameterized using available manufacturer data. [S0022-0434(00)00403-2]

Issue Section:
Technical Briefs
Keywords:
hydraulic control equipment, servomechanisms, valves, nonlinear control systems
Topics:
Flow (Dynamics), Leakage, Leakage flows, Valves, Pressure
1.
Sohl
,
G. A.
, and
Bobrow
,
J. E.
,
1999
, “
Experiments and Simulations on the Nonlinear Control of a Hydraulic Servosystem
,”
IEEE Trans. Control Syst. Technol.
,
7
, pp.
238
–
247
.
2.
Ellman, A., and Virvalo, T., 1996, “Formation of Pressure Gain in Hydraulic Servovalves and its Significance in System Behavior,” Proceedings of the ASME Fluid Power Systems and Technology Division, International Mechanical Engineering Congress and Exposition, Atlanta, GA, FPST-3, pp. 77–81.
3.
Ellman, A., 1998, “Leakage Behavior of Four-Way Servovalve,” Proceedings of the ASME Fluid Power Systems and Technology Division, International Mechanical Engineering Congress and Exposition, Anaheim, CA, FPST-5, pp. 163–167.
4.
Ellman A., Koskinen, K., and Vilenius, M., 1995, “Through-Flow in Short Annulus of Fine Clearance,” Proceedings of the ASME Dynamic Systems and Control Division, International Mechanical Engineering Congress and Exposition, San Francisco, CA, DSC-57, pp. 813–821.
5.
Merritt, H. E., 1967, Hydraulic Control Systems, Wiley, New York, NY.
6.
Thayer, W. J., 1962, “Specification Standards for Electrohydraulic Flow Control Servovalves,” Technical Report 117, Moog Inc.
Copyright © 2000
 by ASME
You do not currently have access to this content.