| Along with the requirement towards longer life,higher reliability and intelligentization of hydraulic products,there will definitely be the main tendency that the working pressure and rotational speed will be higher for the axial piston pump,which is widely used as the power component in a hydraulic system,while the traditional design based on experience is no longer suitable for the high performance axial piston pump.As one of the critical friction pairs,the cylinder block/valve plate pair which consists of a rotating cylinder block and a fixed valve plate is the most part of suction and discharge process as well as the most complicated loading.With the tendency of higher working pressure and rotational speed of axial piston pump,the phenomenon,such as deformation,abrasion,temperature rising and leakage of the mating surfaces of cylinder block/valve plate interface,becomes more highlighted.Therefore,establishing the coupling relationship among the physical fields within the interface,analyzing the influence of operating condition,structure,temperature on the interface lubricating performance,revealing the internal lubrication mechanism would provide theoretical support for developing the high performance of piston pump.According to the general structure of axial piston pump,the dynamic model of the cylinder assembly and the dynamic model of the piston-slipper assembly are established,respectively,the pressing force and the tilting moment acting on the interface are discussed in detail.Standing upon the tipping criterion of the cylinder block,the critical tipping speed is derived,the influence of the conical angle of the piston,the discharge pressre and the swash plate angle on the stability against the cylinder block tipping is analyzed,which can provide a theoretical basis for improving the stability against the cylinder block tipping.Considering the thermoelastic effect and the surface microstructure,the multi-field coupling model for the cylinder block/valve plate interface is established.Based on the whole pump flow model,the dynamic pressure in the displacement chamber is obtained and the short-duration backflow from the flow port within the valve plate into the displacement chamber and the chamber pressure overshoot are discussed.The numerical model of the interface is proposed,combing the micro-motion of the cylinder block by adopting lumped parameters method,the complete forms of Reynolds equation and energy equation with consideration of the pressure-viscosity effect and the temperature-viscosity effect.The Greenwood-Williamson asperity contact model suitable for the interface is put forward standing upon the motion characteristic,which can reproduce the operating condition more precisely.Through the compare among different methods calculating the elastic deformation,the influence method is selected to calculate the elastic deformation as well as the thermal deformation.The heat transfer coefficients of the cylinder block and the valve plate with the attachments are simulated with ADINA,and the thermal boundary conditions are specified,similarly,the pressure boundary conditions are specified with Simulation X.The algorithm suitable for the lumped parameter describing the film thickness is proposed,the cut-off condition is summarized from the actual calculation and the workflow is presented as well as the extension results,and some simulated results are discussed,including the distribution of temperature,the thermal deformation and the pressure deformation,the position drift of the minimum film height and the contact pressure distribution.After establishing the numerical coupling model of the interface,the effect of the operating condition,the boundary temperature and the sealing belt width on the interface lubricating performance is analyzed.The discharge pressure and the rotational speed are qualified as the main parameters based on the axial piston pump performance requirements.The simulation results show that when raising the discharge pressure or slowing down the rotational speed,the interface lubricating performance is becoming worse,specifically,the tilt state,the vibrating motion and the running stability of the cylinder block are aggravated,the contact of the discharge and intake side is strengthened.Furthermore,the discharge pressure affects the symmetry of the temperature distribution,while an increase of the rotational speed can lead to the temperature rising sharply.The same effect is found through one way increase of the sealing belt width,which is the improvement of the interface lubricating performance.At a constant pressing factor,reducing the external sealing belt width is conducive to lowering the temperature,but aggravating the tilt state of the cylinder block.When the boundary temperature rising,the contact and the film temperature are increased,the film bearing capacity is getting worse.The predicting abrasion model is proposed by introducing the classic Archard's theory calculating the adhesive abrasion into the numerical coupling model of the interface,which can export the contacting distribution.The analytical results indicate that the abrasion of the discharge side would be strengthened through increasing the discharge pressure or decreasing the rotational speed,while the abrasion on the intake side increases at first,and then decreases when raising the rotational speed.The maximum abrasion of the discharge side appears at about 135°,while that of the intake side varies from 203.5° to 211°.The abrasion decreases when raising the sealing belt width or reducing the ratio of internal and external sealing belt width,while the maximum abrasion height and the abrasion area increase as the boundary temperature rising.The abrasion height is measured on an actual used valve plate,which shows the numerical model can predict the position of the maximum abrasion precisely,and the further comparison between the actual wear distribution and the predicting results at different operating conditions implies the abrasion occurring at the high pressure and low speed condition.According to the working characteristic of the cylinder block and the valve plate,the experiment form is determined as the whole pump testing and the experimental system is designed and built up.In order not to affect the interface performance,the sensor channels are designed outside of the external sealing belt and the axial position of the cylinder block at different discharge pressure,rotational speed and temperature is measured by three micro eddy current displacement sensors,which reflects the variation of the wedge interface without consideration of the deformation.The measurement results and simulation results have the same trend,which verifies the fluid-structure and thermal coupling model of the interface. |
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