Research And Improvement Of Cavitation Characteristics Of The Parallel External Gear Pump Under Low Temperature

External gear pump has oil trap during the work because of its own structure and working principle,which leads to cavitation easily.Cavitation caused by bubble collapse can damage the gears and floating side plate of gear pump,and reduce the life of gear pump.The working oil temperature is one of the main factors affect ing the cavitation of external gear pump,but current research es on the cavitation of the external gear pump are mostly carried out at normal temperature.In this paper,a parallel external gear pump for special vehicles is studied.The working oil temperature can be as low as-40 ?.Under this low temperature condition,the oil viscosity is very large,the oil absorption of the gear pump is seriously insufficient,the cavitation degree is intensified,and the cavitation process is very different from that at normal temperature.In addition,compared with a single gear pump,the phase difference caused by the asymmetric installation of two meshing gears is also an important factor affecting its cavitation.Therefore,it is of great theoretical value and engineering significance to study the cavitation phenomenon of parallel external gear pump at low temperature and put forward the improvement measures to reduce the cavitation.In this paper,the parallel external gear pump used in the lubrication system of special vehicles is taken as the research object.Firstly,the cav itation researches status of the gear pump are summarized,and the cavitation phenomenon caused by the structure,working principle and the volume change of the trapped oil cavity of the parallel external gear pump is analyzed.Secondly,based on the ?-? turbulence theory,the cavitation process of the internal flow field of the gear pump at-40 ?,which is compared with the cavitation process at 20 ?,is simulated and analyzed by using the full cavitation model.Based on the analysis and study of three factors that affecting the cavitation characteristics of parallel external gear pump(stagger p hase difference,suction port pressure and rotation speed),structural improvement methods to reduce the cavitation strength of parallel external gear pump are proposed,and numerical simulation is carried out.The main research contents and conclusions are as follows:(1)Based on the theoretical analysis of flow pulsation,when the stagger phase difference(the degree of one gear pump being ahead or behind of th e other ones when installed)is 0°,10°,18°,30°,the overall cavitation and outlet flow pulsation of parallel gear pump at low temperature of-40? and normal temperature of 20? were analyzed.The study found that under the condition of low temperatur e-40?,when the phase difference between the two pumps is 10°,the overall cavitation intensity and outlet flow pulsation of the parallel external gear pump are the minimum.Under the condition of normal temperature 20?,when the phase difference between the two pumps is 18°,the overall cavitation intensity and outlet flow pulsation are the minimum.(2)Under the condition of low temperature-40?,the flow pulsation and gas volume content at the outlet of gear pump change with the ch ange of rotating speed.When the rotating speed increases from 500 r/min to 1500 r/min,the outlet flow pulsation increases gradually.At-40?,the average gas volume content of gear increases from 5% to 28%,while the average gas volume content at 20? remains about 1.3%,which indicates that the effect of rotating speed on cavitation is more obvious at low temperature than that at normal temperature.(3)Under the condition of low temperature-40?,the flow pulsation and gas volume content at the outlet of gear pump change with the change of the oil suction port pressure.When the pressure of oil suction port increases from 0.1 MPa to 0.3 MPa,the average volume flow of oil outlet gradually increases.Under the condition of low temperature-40?,the average gas volume content of gear part reduces from 51% to 41%,while that of normal temperature 20? reduces from 7% to 2%.The results show that increasing the suction port pressure can reduce the cavitation intensity of the gear pump.(4)Combined with the structural characteristics and practical conditions of the parallel external gear pump,a structure to reduce the cavitation intensity of the pump by opening a symmetrical cat-eye unloading groove on the floating side plate of the pump,optimizing the pump oil flow channel and adding gear relief grooves ways to improve.The results show that the above measures can effectively reduce the cavitation intensity of the gear pump,and provide a useful reference for the structural optimization design of the parallel external gear pump.