Use of phase portraits of hydro-mechanical units for diagnosing aircraft hydraulic systems

The article deals with diagnostics of hydraulic systems using phase portraits. A brief review of the existing methods for diagnosing hydraulic units identifying their advantages and disadvantages is given. An approach based on the analysis of dynamic characteristics of a hydraulic system and phase portraits of hydro-mechanical units in their operational and faulty conditions is proposed. As an example, we consider a dynamic model of a simplified hydraulic system consisting of standard components. By adjusting the model parameters characteristic faults typically occurring in operation, such as internal leaks in the pump, contamination of the hydraulic fluid with mechanical impurities, sticking of the valve, etc. were artificially introduced in hydro-mechanical units. A family of phase portraits of a hydraulic system for the operational condition and various faulty ones was constructed. A quantitative estimate of their changes, based on calculating the difference in the areas of the figures restricted by their graphs, is proposed. As a result, it was established that failures and malfunctions introduce changes in the phase portraits of hydro-mechanical units, which makes it possible to apply the proposed approach as a basis for diagnosing the technical condition of hydraulic systems

Set-theory model of the aircraft hydraulic system working fluid state

The article is devoted to the development of a set-theory model of the aircraft hydraulic system working fluid state using the mathematical apparatus of the set theory. The relevance of the work is connected with the necessity of developing a universal mathematical model of the hydraulic fluid state. The model is to form the basis of an intelligent system to control the working fluid state on board the aircraft. As a result, a general expression is obtained that allows describing the working fluid state at an arbitrary moment of time using its basic parameters, namely contamination, viscosity, density, chemical and temperature properties. A hierarchy of parameters of the working fluid state taking into account the diagnostic value of the information obtained during their measurement is constructed. The main classes of states are distinguished among all possible states of the working fluid. These are the ideal state, the normal state, pre-failure and failure. Each of them is described by a set of configurations of all possible values of the main parameters. А technique for optimizing the time of the inspection of technical condition based on the calculation of the change in the entropy of the working fluid is proposed

Prospective lines of improving the process of evaluating the technical condition of aircraft hydraulic system working fluid

The article is devoted to the evaluation of the technical condition of aircraft hydraulic system working fluids. Working fluid parameters (concentration of impurities, viscosity, density, anti-oxidation, anti-wear and thermal properties) determining its technical condition are selected on the basis of a study of scientific and technical literature. The peculiarities of the existing process of its evaluation are discussed. A structural grapho-analytical model reflecting the condition of the working fluid was developed. The model takes into account the influence of the fluids basic parameters as well as reachability and counter-reachability matrices. Analyzing the results, it was found that the graph components are strongly interconnected. Viscosity is closely linked with anti-wear and thermal properties, while variations in mechanical impurity content in the working fluid cause variations in the rest of its parameters. Thus, we can say that the assessment of the working fluids condition based on measuring only its purity and viscosity is not quite reliable. We substantiate the future line of research with the aim of developing new methods to assess the condition of the working fluid, namely, development of mathematical models of the working fluid condition taking all its components into account

Calculating the dynamic error in measurement of electrohydromechanical system parameters, taking into account the operating speed of sensors

It is necessary to ensure appropriate information content of the measuring instruments used for intelligent diagnosing systems of energy and technological complexes based on the measurement of dynamic parameters. Sensors and measuring equipment should possess sufficient accuracy, reliability, speed and consistency of performance. Types of sensors for measuring dynamic parameters are selected depending on the systems structure. They can be, for example, sensors for the electrohydromechanical systems of these complexes, pressure sensors, as well as sensors of flow and temperature of the working media, displacement of moving elements and vibration of the base members. The type of sensor intended for use in the diagnostic system is largely determined by the dynamics of the processes taking place in it. It is necessary that the sensors satisfy their performance requirements. If the sensors have lower speed than is necessary for the process dynamics in the electrohydromechanical system, it can lead to dynamic measurement error and an error in the diagnostics of technical condition. In technical literature, the requirement for the sensor speed is indicated by the fact that it should be an order of magnitude higher than the dynamics of the processes occurring in the system. This approach is not acceptable for choosing the type of sensors for diagnostic systems, taking into account the process dynamics. Firstly, sensors for measuring with this required parameter may not be available. Secondly, even if there is a sensor with a parameter close in speed to the dynamics of the system processes, it is necessary to know in advance what dynamic error it can lead to and how it will affect the accuracy of the diagnostic system. An analytically generalized dependence of the dynamic measurement error of electrohydromechanical system parameters on the relative sensor speed is obtained in this paper. This dependence allows you to choose a sensor with a dynamic error that does not exceed a given value. The calculation of the dynamic measurement error is shown using the MI-8 helicopter hydraulic system as an example