The Research On Thermal Deformation Of Clearance And Particle Distribution Inside Hydraulic Valve

Hydraulic spool valve is one of key components of hydraulic power transmission and control system,which is widely applied in hydraulic system.However,as science and technology advances,the faults for hydraulic spool valve are constantly improving,particularly the clamping for hydraulic spool valve induced by viscous dissipation and particle motion,this has massive influence on the hydraulic system.However,in the process of using hydraulic valves in medium and high pressure system,often appears spool valve jam phenomenon.The main reason is owing to viscous heating when fluid flows through the spool valve port,which causes the temperature increasing of part of oil,the thermal expansion of the spool and the decreasing of the matching clearance of spool and body.Meanwhile,solid particles gathered in pressure groove clearance,which would be likely to cause the phenomenon of spool clamping,posing a threat to security and ride performance of hydraulic system seriously.Based on fluid-solid coupling conjugate heat transfer method,the further research on multi-physical fields among viscous heating,flow and heat transfer,thermal deformation and particle motion inside spool valve was carried out by the conjugate heat transfer module and solid mechanical module of COMSOL code software in this paper.The results indicated that,the high temperature mainly appeared at the zone with larger velocity gradient and the surface of throttling grooves of spool impacted by the high-velocity flow.a radial non-uniform annular embossing was occurred in grooves of spool zone,the matching edges of valve core and valve body were employed with parabolic radial thermal expansion,and the solid particle gathered densely in pressure groove of gap.As a result,it was more likely to cause spool clamping.The main contents of this paper are as follows:In the first chapter,the background and significance of this thesis was presented.The phenomenon of hydraulic clamping and the spool clamping caused by particle contaminant was introduced.The history and current progress on thermal-mechanical coupling and sticking for contamination of hydraulic spool valve at home and abroad was reviewed.In the second chapter,the functions and applications of COMSOL software were introduced briefly.The built-in parameters of the calculation module were analyzed.The theoretical basis of viscosity temperature rise inside spool valve was presented.The calculation equation of orifice area was proposed based on the structural characteristics and the equivalent orifice area theory,and the numerical analysis of flow and heat transfer inside spool valve with various forms of groove was carried out.In the third chapter,the global thermal-mechanical coupling numerical simulation model of spool valve with fluid domain and solid domain was established.The temperature distribution field and thermal deformation law under typical working conditions were studied.The influence of these actual factors consisting of viscosity-temperature characteristics,oil with bubbles and the linear relationship between thermal conductivity and temperature on the viscous temperature rise and thermal deformation of spool valve was investigated.According to above evidences,spool secondary structure was improved to reduce the radial thermal deformation of spool.In the fourth chapter,the whole thermal characteristics of 2 D model of the spool valve with different kinds of pressure groove were established.The effect of vital factors such as operating pressure,valve opening,and fitting clearance size on thermal characteristics of the fitting clearance of spool valve was analyzed.In the fifth chapter,the two-dimensional symmetric model for the original gap and gap with thermal deflection with various forms of pressure groove of the spool valve was established.The effect of the radial clearance structure on the particle distribution and the trajectory was studied.The integrated mechanism of these two actions was revealed.