| Multi-way valve is the important control component of the loader hydraulic system.Additionally,spool valve is the key part of multi-way valve.Flow force is difficult to be calculated and it's one of the main elements which would cause spool clamping.For 3 way 6 port opening center hydraulic valve,flow force will influence the control performance of spool valve and even lead to spool clamping when it is too large,which directly influence the reliability and security of actuator.So it is significant to reduce the flow force of spool valve for improving the control performance of the loader.To study the flow force of multi-way valve,the joint simulation method of AMESim and FLUENT was adopted.The simulation model of hydraulic system of bucket was established,the flow curve was embedded into AMESim system.According to the simulation results,the flow curves and the characteristic curves of important ports in reset process of spool valve are obtained.The flow curve for different port was discretized as the boundary conditions of FLUENT simulation,and then the flow force in reset process of spool valve was calculated.The result shows: in the reset process of spool valve,the peak value of flow force always occurs in the particular position,and the flow force is oriented to the direction of spool movement.At the same time,the heaver the loading pressure is,the larger the flow force is,and the micro-moving performance of spool is easier to be influenced.Besides,in the opening process of spool valve,the flow force of spool valve only comes from P-T port,and the value has nothing to do with loading pressure.Moreover,the peak value of flow force always occurs in the particular position,and is larger than the value of reset spring force,which will lead to spool clamping because the flow force is oriented to the opposite direction of spool movement.To solve the problem of the excessive flow force which lead to spool clamping in reset process,three kinds of structure are introduced to improve the situation,and the simulating calculation and theoretical analysis are adopted to verify the improvement effect.The result shows that three structures could reduce the peak value of flow force by 17.8%,60.6% and 61.6%.Besides,structure? and structure? could reduce the peak value of flow force down to the value of reset spring force,thus the spool clamping caused by flow force could be avoided.The main contents of this thesis are as follows:In chapter 1,the background,the purpose and the significance of this thesis are raised.Current research and issues of flow force for spool valve in china and abroad are concluded,the application of flow simulation technology in the field of hydraulic element research are described,and the main research contents of this paper are summarized.In chapter 2,the opening center hydraulic valve used in loading pressure is taken as reference model,and the inner structure of multi-way valve is introduced.In the bucket lifted condition,the principle of control process for spool valve is analyzed.The AMESim hydraulic system is established and the proportion of orifice is defined.Flow and pressure curves of P-T,P-A and B-T ports in the reset and opening process of spool valve are obtained under different loading pressure,then the flow curves of different ports are discretized as the boundary conditions of FLUENT simulation.In chapter 3,3D models of spool valve and valve body are generated and assembled by taking loading pressure bucket spool valve as reference,and the flow field models of P-T,P-A and B-T port are extracted.In the reset process of spool valve,the flow force of P-T,P-A and B-T port are calculated by FLUENT under different loading pressure and different inlet flow value which was discretized.Furthermore,the flow force of different ports are overlapped to generate the resultant force of spool valve in different loading pressure.In chapter 4,in the opening process of spool valve,flow field simulation and calculation of flow force are generated by FLUENT software under different inlet flow value which was discretized.Furthermore,the velocity distribution,the streamline distribution,and flow force value are analyzed.In chapter 5,to solve the problem of spool clamping caused by the peak value of flow force in reset process of spool valve,three kinds of structures are proposed,which are divided into three classes: cone stem spool,ring cavity inside the valve body,and fluid jet guidance baffle.These three kinds of structures are analyzed by simulation and calculation to verify the effects for reducing the peak value of flow force. |
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