On using unstable electrohydraulic valves for control

High bandwidth, high flow rate electrohydraulic valves typically have two or more stages. Multi-stage valves are expensive, require meticulously clean fluid, and introduce higher order dynamics. Single stage spool valves are cheaper and more reliable. However, they are not suitable for high bandwidth, high flow rate applications due to limitations of the stroking actuators. In this paper, we investigate the feasibility of reducing this limitation by designing the valve to be open loop unstable. This can be accomplished by exploiting the transient flow forces. Simulation case studies indicate that the unstable valve provides faster response than the stable valve when stroking forces are limited. Moreover, the unstable valve tends to require less power and work to operate.