Investigation Into Flow Coefficient Of Orifice And Calculation Of Steady Flow Force Of Spool Valve With Notches

Spool valve with notches is one of the basic constructions of hydraulic valve,which places several notches axisymmetrically on the spool to form the restriction configuration. This type of valve is widely used in direction and velocity control for hydraulic actuators. Spool valve with notches is widely used as the main valve element in hydraulic control valve of construction machinery or hydraulic proportional valve or servo valve.Multilevel range of orifice area can be obtained by deploying the notches,so that flow rate can be multi-throttling controlled to satisfy the demand velocity of movement of hydraulic actuator in different operating operation.When in state of starting or stopping operation,the hydraulic actuator can work steady by moving the spool in its precise operation range.On the other hand,in state of working operation,the hydraulic actuator can work quickly or proportionally by moving the spool in its quick or proportional operation range.Investigation into flow characteristics of orifice and calculation of flow force of spool valve with notches is of great significance to designing high quality hydraulic control valve.In this thesis,experimental analysis,numerical simulation and theoretical analysis were used to investigate the flow characteristics of orifice and the calculation method of flow force of spool valve with notches.A principle to calculate the orifice area of two typical notches in spool valve was proposed,which the orifice area of constant section notch is determined by resistance effect of two stage orifices with two throttling cross-section in series and the orifice area of diverging section notch is specified by the minimum section along the notch pass.A principle to calculate the orifice area of combined notches was proposed,which is based on the serial and parallel effects of fluid flowing along the notches.Then the correspondence calculation formulas to calculate the orifice area of the above-mentioned notches was deduced and a general computational program to calculate the orifice area of spool valve with notches was developed.The value of flow coefficient(simply called Cd)of orifice in spool valve with rectangular notch changes with the spool displacement,when the displacement is small,the Cd is near to 1 and then decrease steeply with the displacement increment,when the displacement is near to full length of the notch,the Cd will increase with the displacement increment,the Cd is near a constant in the middle range of the spool displacement.The Cd increase when the ratio of depth to width in cross-section of the rectangular notch is large,and increase in some degree when the hydraulic diameter of the cross-section is large.The Cd in flow-out direction is larger than that of flow-in,the difference is about from 0.05 to 0.1.The value of Cd of orifice in spool valve with slope notch decrease with the spool displacement, the Cd is the exponential function of spool displacement.The Cd decrease when the slope angle of the notch is large.The Cd in flow-out direction is larger than that of flow-in,the difference is about from 0.1 to 0.3.A new concept of"orifice area of flow control" to define the flow control function of orifice is established which is the function of orifice area and flow coefficient.The digital calculation model and computational procedure of steady flow force of spool valve with rectangular notch was obtained.The research results presented in this thesis have showed the importance in both practice and theory for the digital design and precise performance prediction of spool valve with notches.The main content of this thesis is as follows:In chapter 1,the background and significance of this thesis was presented.The history and current research progress on flow rate and flow force of hydraulic valves were reviewed.The application of CFD to investigate the hydraulic component was summarized.Lastly,the main research subjects were presented.In chapter 2,aimed at the two typical notches of equal section notch and diverging section notch in spool valve,based on the configuration feature and the flow pattern in the notches,a principle to calculate the orifice area of spool valve with notches precisely was proposed, which the orifice area of equal section notch is determined by resistance effect of two stage orifices with two throttling cross section in series and that of diverging section notch is specified by the minimum section along the notch pass.A principle to calculate the orifice area of combined notches was proposed,which is based on the serial and parallel effects of fluid flowing along the notches.Then the correspondence calculation formulas to calculate the orifice area in above-mentioned notches was deduced.The orifice area of spool valve with notches can be got using the superposition principle.A general computational program to calculate the orifice area of spool valve with notches was developed.The research results presented in this chapter is the basis of the next research of flow coefficient of orifice and calculation method of flow force of spool valve with notches.In chapter 3,the flow coefficient of orifice of spool valve with rectangular notches or slope notches or combined notches was investigated.Based on the experiment of flow characteristics,the orifice area can be calculated by the computational procedure,so that the flow coefficient of orifice of the above-mentioned notches can be obtained by using numerical analysis.Some important conclusions about flow coefficient of orifice in spool with notches had acquired,and the reference values in engineering design was provided.A new concept of "orifice area of flow control" to define the flow control function of orifice is established which is the function of orifice area and flow coefficient.The orifice area of flow control describes more reasonable the function of orifice to flow control than the tradition concept about orifice area and coefficient. In chapter 4,flow force of spool valve with rectangular notches was investigated by experiment analysis.It was shown clearly that the flow force has close relationship with spool displacement,configuration feature of notch and flow direction in notch.Author used CFD to simulate the pressure and velocity distribution in spool valve with notches,combined with Hydro-mechanics momentum theorem,explained the characteristics of flow force throwing the flow characteristics in spool valve with notches.Based on both flow characteristics in notches,combined with the results of experiment and CFD simulate,the digital calculation method of flow force was investigated.The digital calculation model and computational procedure of flow force was obtained.It was shown that the results of the computational procedure closely with the results of experiment.In chapter 5,aimed at the vibration problem of flow amplifier steer system in the loaders, the characteristics of flow amplifier valve which is the main control valve in steer system was analyzed digitally,then the reason of the vibration problem was analyzed.Author used the present research conclusions in this thesis,studied on the new design of the flow amplifier valve.A new flow amplifier valve was designed successfully.It was shown by practical Vibration Test that there were little vibration,good control performance,good operator comfort and energy-saving with the new flow amplifier steer system.In chapter 6,some conclusions in this thesis were summarized and the future research proposals were suggested.