Electro-hydraulic pressure-control valves are used in many applications, such as manufacturing equipment, agricultural machinery, and aircrafts to name a few. They are often used to actuate hydraulic clutches, such as those found in power shift transmissions. A traditional pressure-control valve with open-loop control algorithm is typically used in clutch applications. This scheme often results in inconsistent or undesirable system behavior due to the nature of open-loop control as well as the nonlinear system dynamics and uncertainties. In this research two new electro-hydraulic pressure-control valves were designed in order to decouple the valve and control port (hydraulic) dynamics. This was achieved by removing the regulated pressure balancing force utilized in traditional pressure-control valves. Different closed-loop controllers were designed and tested in parallel in order to achieve the desired steady-state and dynamic regulated pressure response. A nonlinear dynamic model was developed for each valve then used to compare the performance characteristics of the valves. Linear analysis was performed and various control techniques were studied from classical PID control to modern optimal control. The model was also used to predict performance of the closed-loop controllers prior to experimental testing and to validate experimentally tuned controllers afterwards. Prototype valves were fabricated in order to validate the model and to test the controller designs experimentally. Different valve and controller combinations were compared to a traditional pressure-control valve utilizing open-loop control through typical industry performance tests. This study found that a valve with a traditional pressure-control pilot and a main stage spool with no pressure balancing force, along with a gain scheduled PID controller, outperformed the traditional valve in all areas tested. This approach is also feasible within the existing infrastructure of most applications where the benchmark traditional valve is currently used.

This book shows an independent metering electro-hydraulic control system involving its flexible hardware layouts, complex software control, representative products and applications. The book includes one chapter introducing the background and motivation of the independent metering electro-hydraulic control system. It also includes one chapter to summarize various hardware layouts involving the utilized hydraulic components and circuits, as well as analyze their advantages and disadvantages. It emphatically consists of four chapters demonstrating the detailed multivariable control strategies from three levels: load, valve and pump, together with fault-tolerant control under the fault condition. It includes a last chapter, in which products of independent metering control valve and their applications in some typical heavy-duty mobile machinery are collective works of reviews illustrative of recent advances. This book is interesting and useful to a wide readership in the various fields of fluid power transmission and control.