| A new methodology for the conceptual design of hydraulic system based on the energy characteristic state space approach is developed. The goal is to solve the problem of hydraulic system conceptual design by establishing a mathematical model. This research is supported by the National Natural Science Foundation of China under Grant No. 50775016 and the National High Technology Research and Development Program of China (863 program) under Grant No. 2006AA04Z101.The energy characteristic state description for hydraulic system is established first. The energy characteristics of hydraulic system are represented by energy characteristic state vectors which are formed by abstracting the quantitative and qualitative characteristics of energy parameters such as pressure, flow, force, and velocity. The hydraulic system is regarded as a set of subsystems with single action, and the working process for each single-action subsystem is simplified as a linear transformation of the energy characteristic state vectors.Two categories of basic transformation units are defined by combining the energy adjustment components, such as pump, cylinder, pressure control valves, and flow control valves, with their usage patterns in the circuits. The energy characteristic state transformation equations for the basic transformation units are then established according to the function analysis. The coefficient matrices of the equations are obtained as the representation of the basic transformation units. By surveying all commonly used energy adjustment components and the patterns of their usage, a library of basic transformation units are defined and their matrix representations are also compiled. Thus, the database of physical units for the conceptual design of single-action subsystem is established.The conceptual design model for single-action subsystems based on the energy characteristic state space is established. By establishing the energy characteristic state space, the design process is transformed into the model space. According to the input and output energy characteristic states of a subsystem, the energy characteristic state transformation equation of subsystem is established, and the coefficient matrix of the equation can be obtained to describe the subsystem. The subsystem matrix is the product of the characteristic matrices of the basic transformation units. Thus, the characteristic matrix of a subsystem can be successively decomposed into various sets of characteristic state matrices of basic transformation units. Each set of such basic transformation units is the topological representation of a hydraulic system. By successive decomposition of a system matrix, a thorough conceptual design process for single-action subsystems is established.Basic combination units are defined to describe the connectional functions of the directional control valves. The connection state graphs and the connection state matrices are established to represent the functional knowledge of basic combination units. By surveying all independent structures of 2-5 ports basic combination units, a library of physical units for the combination design of multiple sub-circuits is established.A synthesis model for multiple sub-circuits based on graph mapping is established. The circuit diagram for each subsystem is abstracted to a directed connection state graph that describes the connectional relationships of the components contained in it. The directed connection state graph of system is then formed by merging the ones of the subsystems. After a series of simplification operations, the simplified connection state graph of system is expanded by subsystem sequences. For each expanding sub-graph, the connection state graphs of basic combination units which have the same structures are identified. The directional control valves can then be formed by the obtained basic combination units, and the mapping relationships between the system components and the valve ports on the directional control valve are also established. Thus, the entire circuit of the system is formed. The associated matrix operations are also proposed.The proposed method is illustrated by a design instance. With the model, large numbers of feasible schemes can be generated automatically by matrix and graph operations. Although practical schemes are normally limited, plentiful suggestive schemes can widen the designer's mind and provide a foundation of innovative design. It offers the first mathematic tool for the qualitative description of a hydraulic circuit and thus paves the way for the automated conceptual design of hydraulic systems.
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