| This topic comes from a project of a research institute.The purpose of this project is to develop a mathematical model used to describe the relationship between friction force of electro-hydraulic servo valve spool pair and temperature,pressure and speed,and to study the relationship between friction force of the servo valve pair and temperature,pressure and speed through simulation analysis and experiments.Furthermore,the experimental results of the friction force of the servo valve pair are analyzed,and the relationship between the friction force and the factors such as temperature and speed are obtained,which play a positive role in guiding the optimal design,production and accurate control of the servo valve pair.The three-dimensional model of the servo valve pair is established by analyzing the complex structure of the electro-hydraulic servo valve pair.The mechanism and characteristics of friction force of the servo valve pair are analyzed and studied in combination with the working conditions,based on the material properties and structural characteristics of the valve spool and sleeve.Based on the features of influence of work conditions on friction force,the influence is divided into two aspects:the radial uniform expansion and the non-radial expansion.Under the conditions of low pressure and uniform heating,servo valve pair expands evenly in radial direction.The influence of temperature and speed on the friction force of the servo valve pair is mainly studied since the pressure has little influence.In this case,the friction of servo valve pair under the influence of temperature is mainly related to two factors:e.g.(1)the friction of the valve spool and the sleeve(2)the friction of the spool and the oil.In this paper,the mathematical model of friction among temperature,valve spool and sleeve are established by studying the relationship of the direct contact area of the valve spool and sleeve with the temperature,the relationship of the critical shear strength of the material adhesion point and the temperature,respectively.The mathematical model of the direct contact friction of the valve spool and sleeve with temperature is established.By analyzing the relationship of viscosity of aviation hydraulic oil and temperature,the mathematical model of friction force of valve spool and aviation hydraulic oil with temperature is obtained.LuGre friction model is used to study the relationship between speed and friction of servo valve pair.Under the condition of high pressure and uneven heating,the servo valve pair does not expand uniformly in the radial direction.In this case,temperature and pressure are the main factors that influence the friction of servo valve pair.The influence relation of temperature and pressure on the friction force of servo valve pair is deduced theoretically.The Bowden friction model is used to establish the mathematical model of servo valve pair friction force,temperature and pressure,respectively.The friction force of servo valve pair under the combined action of temperature and pressure is simulated and analyzed.Experimental research on friction characteristics of servo valve pair is carried out,and the experimental device is designed to study the friction characteristics of servo valve pair.The static and dynamic friction parameters in LuGre friction model are identified according to the Stribeck curve fitted by the friction values of servo valve pairs working at different speeds.The friction force of the servo valve pair working at different temperatures is measured experimentally.The results show that the mathematical model of temperature and friction of servo valve pair can accurately describe the relationship between temperature and friction of servo valve pair. |
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