| In comparison with the conventional valve commutating piston pump in which swash-plate is rotating,cylinder block is stationary and the intake valve and the outlet valve are mounted in the barrel of pump,a new kind of double-swashplate hydraulic axial piston pump with valve commutation in which two swash plates were fixed face-to-face in a housing across the cylinder block,and port valves were nested in the cylinder block and rotated around the shaft centerline,obviously has different working principles.It is necessary to pay attentions to the effects of centrifugal force and Coriolis force acting on the rotating valve body and the fluid mass adjoined with,and to study the influence of centrifugal force and Coriolis force on pump output flowrate characteristics.The experimental device for simulating the working conditions of the rotating valve at fixed opening is used to investigate the flow characteristics and the flow coefficients in different flow directions and different speeds.Considering a disc valve which has 16 mm diameter of seat core,17.5 mm diameter of disc-plate and the 1 mm opening as the sample,it is found that the flow coefficient increases from 0.619 to 0.746 in centrifugal flow direction and the reverse flow coefficient decreases from 0.614 to 0.547 as the speed rises from 0 rpm to 1800 rpm.The mathematical model of the flow field of rotating disc valve port was established,the flow characteristics and flow pattern of disc valve port were simulated by using finite element method.Obtaining the velocity nephogram,velocity vector graph and velocity distribution curve of the valve port,the effects of rotating speed,flow direction and opening of valve port on the flow pattern are studied.The results show that the centrifugal force generated by the rotation gives energy to the fluid so that the fluid in centrifugal flow direction through the valve port requires less pressure difference than that of the conventional valve commutation,by contrast,the fluid through the valve port encounter greater resistance in the reverse flow.Coriolis force makes the velocity distribution appear significant non-axial symmetry or uneven distribution in the upstream and downstream of flow control cross section of valve port.Coriolis force and centrifugal force make the fluid move spirally and centrifugally in the chamber before the valve port.Based on the results of experimental research and numerical simulation above,considering the centrifugal force of the valve body and the fluid mass in the front chamber of the valve port,and on the basis of the variation of flow coefficients in different flow directions,rotating speeds and opening of valve port,as well as the effect of centrifugal force equivalent to static pressure acting on the valve plate,and using the control volume method with variable volume and momentum theorem to establish the mathematical model,which match the structure and parameters of the commutation mechanism of the present existed prototype pump.By comparing the numerical simulation results with the experimental results of the prototype pump,the rationality of the factors such as the dynamics of the complex flow of the rotating valve port and the validity of the mathematical model are proved.At the same time,it is concluded that centrifugal force can increase the opening of the valve port,but increase the phase lag angles of the closing of the intake valve.So increasing the spring stiffness of the intake valve can not only offset the influence of the centrifugal force from the valve body and the fluid mass,but also reduce the phase lag angles of intake valve.It is necessary to further study how to rationally exert the centrifugal force and Coriolis force to improve liquid filling efficiency in the process of intake and makes the fluid move more smoothly. |
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