| Gear pumps are widely used as the main driving components in hydraulic system,such as construction machinery,aerospace,medical chemical and other fields.With the increasingly high requirements for the stability of hydraulic system in various industries,the high efficiency and low pulsation of gear pumps have become the main trend of their development.The circular arc gear pump improves the gear end face profile,which distinguishes it from ordinary involute gear pumps.It improves the trapped oil phenomenon from the gear structure and can greatly reduce or even eliminate the inherent flow pulsation of volumetric pumps,greatly improving the pump’s operating stability.This article focuses on circular arc fuel gear pumps.Its tooth top and tooth root are smooth circular arcs,connected by involutes in the middle.During operation,there is no trapped volume between gears,and the transmission is stable,especially at high pressures and speeds,it can still maintain a relatively stable operating state.However,due to its complex gear structure,only specific geometrical parameter values can achieve good operating conditions,otherwise the opposite trend will occur.Based on this,this article establishes a mathematical model of the "circular arc-involute-circular arc" tooth shape based on coordina te transformation,analyzes the feasibility of its meshing transmission,establishes the mathematical model of the total coincidence degree,and then establishes the mathematical model of the instantaneous flow rate and gear force of the circular arc gear pump.It explores the geometrical factors that affect its internal flow and gear force.Based on this,4 sets of circular arc gear pumps with different helix angles and numbers of teeth were selected to explore the influence of the helix angle and the number of teeth on the internal flow characteristics under different inlet and outlet pressure differences and operating speeds.The three-dimensional simulation software Pump Linx was used to explore the change of the internal flow field of the circular arc gear pump during rotation.During this period,a closed experimental platform for circular arc gear pumps was built to measure the volumetric flow rate of the sample machines under different inlet and outlet pressure differences to verify the accuracy of numerical simulation.Based on the NSGA-II genetic algorithm,the multi-objective geometric parameter optimization design was carried out to promote the circular arc gear pump to turn to the actual application faster.Through the analysis of the internal flow field of the circular arc gear pump under different geometrical parameters and its multi-objective optimization design,the results are as follows:(1)Increasing the helix angle has a significant impact on the outlet flow characteristics of the circular arc gear pump.When the helix angle gradually increases from 23.74° to 39.24°,the average flow rate value of the pump outlet first increases and then decreases.Under the conditions of 6MPa and 1450 rpm,the volumetric efficiency of the pump with helix angles of 23.74° to 39.24° is 72.64%,73.96%,74.40%,and 73.09%,respectively.As the helix angle increases,the instantaneous flow rate pulsation coefficient of the pump outlet decreases,and even at high pressures,larger helix angles can still maintain lo wer flow rate pulsation values.(2)The decrease in flow rate pulsation coefficient is not linear with the increase of the number of teeth.The numerical simulation of the 7-tooth gear pump has the largest average outlet flow rate.The theoretical instanta neous outlet flow rate of the9-tooth gear pump is the smallest.Under the conditions of 8MPa and 2000 rpm,the volumetric efficiency of the 7-9 tooth gear pumps changes by +18.34%,+7.15%,and+20.70% compared to the 6-tooth gear pump,respectively.(3)Using the NSGA-II genetic algorithm to perform multi-objective optimization design on flow rate pulsation coefficient,displacement,and volume objectives.By comparing the flow performance of the circular arc gear pump before and after optimization through CFD numerical simulation,the flow rate pulsation coefficient of the optimized circular arc gear pump is reduced compared to before optimization,and the overall hydraulic performance is improved.Overall,increasing the helix angle and the number of teeth has a positive effect on reducing flow rate pulsation,improving outlet flow rate(or volumetric efficiency)during the operation of the circular arc gear pump,tending to stabilize the pressure distribution in the pump chamber,reducing pressure differen ce between adjacent teeth,tending to stabilize the flow state in the pump chamber,tend to make the gear diameter and axial force uniform,and tend to reduce gear force pulsation.However,this positive effect is not a linear change with a single factor,but a superposition of the variable and related factors.Therefore,there is always an optimal geometric parameter for the stable operation of the pump according to different operating conditions or requirements.This article establishes a quantitative rel ationship between gear geometrical parameters(helix angle,number of teeth,tooth width)and circular arc gear pump flow performance(flow rate pulsation coefficient,displacement,etc.),analyzes the outlet flow(pressure)characteristics,pressure distr ibution in the chamber,and gear force distribution rules,and optimizes the geometric parameters to provide a theoretical basis for selecting circular arc gear pumps in the future. |
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