A review of electro-hydraulic servovalve research and development

Abstract

This paper provides a review of the state of the art of electro-hydraulic servovalves, which are widely used valves in industrial applications and aerospace, being key components for closed loop electrohydraulic motion control systems. The paper discusses their operating principles and the analytical models used to study these valves. Commercially available units are also analysed in detail, reporting the performance levels achieved by current servovalves in addition to discussing their advantages and drawbacks. A detailed analysis of research that investigates these valves via computational fluid dynamic analysis is also provided. Research studies on novel control systems and novel configurations based on the use of smart materials, which aim to improve performance or reduce cost, are also analysed in detail.

Research and Development of Electro-hydraulic Control Valves Oriented to Industry 4.0: A Review

“…Since then, Moog, Rexroth, and other hydraulic component manufacturers have introduced single flapper-nozzle valves, dual flapper-nozzle valves, jet-pipe servo valves, and other products. As a result, electro-hydraulic servo valves are used in aerospace, military defense applications, industry, automation, and a wide variety of other fields [28], as demonstrated in Figure 6(a) and (b). The spool and sleeve of the servo valve need to be precisely matched, which makes it costly to manufacture.…”

A Novel Servovalve Pilot Stage Actuated by a Piezo-electric Ring Bender: A Numerical and Experimental Analysis

“…The architectures of commercially available two-stage servovalves have not substantially changed for many years, since they can provide high reliability and excellent dynamics [1]. Most valves make use of either a double nozzle-flapper pilot stage or a deflector jet pilot stage depending on the applications, the former being more used in industrial applications, whilst the latter is more frequently used in aircrafts [2]. Regardless of the pilot stage, the main stage is usually a spool valve in which the main spool is actuated by a differential pressure generated at its extremities by the pilot stage.…”

“…Regardless of the pilot stage, the main stage is usually a spool valve in which the main spool is actuated by a differential pressure generated at its extremities by the pilot stage. In this way, very high actuation forces are generated, providing fast respond speeds and capability of shearing chips that might be jammed between the metering edges [2]. The force levels developed are much higher than proportional valves or on/off valves using solenoids to directly drive the spool [3][4][5][6][7][8][9][10], which results in a much faster response and higher shear forces.…”

“…(1) The pilot stage requires a quiescent flow rate to work, to be referred to as the internal leakage of the pilot stage (note that the overall internal leakage is the sum of this contribution and a second contribution given by the internal leakage in the main stage). Although it is small compared to the nominal flow rate of a valve, the internal leakage in the pilot stage is continuous and constant regardless of the opening degree of the main stage, thus causing unwanted power consumption during operation [1,2]. (2) The electromagnetic torque motor assembly is also a major issue associated with these valves because it is composed of many sensitive mechanical and electrical parts that penalise simplicity, set-up, duration of manufacture and manufacturing costs.…”

“…Although it is small compared to the nominal flow rate of a valve, the internal leakage in the pilot stage is continuous and constant regardless of the opening degree of the main stage, thus causing unwanted power consumption during operation [1,2]. (2) The electromagnetic torque motor assembly is also a major issue associated with these valves because it is composed of many sensitive mechanical and electrical parts that penalise simplicity, set-up, duration of manufacture and manufacturing costs. Of these components, the flexure tube, used to support the flapper while separating the torque motor from the hydraulic fluid, is the most critical.…”