Numerical Model Based Research On The Flowrate And The Radial Lubrication In Internal Gear Pumps

Internal gear pumps(IGPs)are becoming more and more popular in many applications such as high-end machine tools,molding machines,marine equiptments and aerospace due to their advantages in terms of compactness,low flow ripples and low noise level.However,the domestic IGP market is largely occupied by foreign manufacturers,and the domestic manufacturers are putting efforts into the repeated trial and error process,which results in poor performance of IGPs.This thesis is focused on the IGPs' fluid-structure interaction(FSI)models accounting for design methods for the purpose of improving the performance of IGPs.This thesis proposes a simulation approach for IGPs,including a lumped parameter model for analysis of the pressure and flow characteristcs,and lubricating models for the radial lubricating interfaces including the ring-gear/case interface and the gear-shaft/journal-bearing interface,starting from the geometric modelling of the pump.The proposed model was validated by experiments on IGPs from the aspects of the outlet pressure ripples and the leakage of the lubricating interfaces.The proposed model allows the analysis of the IGPs'performance in terms of the outlet flow ripples,the lubricating characteristics of the ring-gear/case interface and the gear-shaft/journal-bearing interface.Simulation results suggest that the outlet flow ripple decreases as the operating speed increases and increases as the load pressure increases.Apart from that,the trapped flow yields a decrease in the outlet pressure and flow ripples while the the transitional flow yields an increase in the outlet pressure and flow ripples.Regarding the ring-gear/case interface,simulation results suggest that the supporting force resulting from the fluid film's hydrodynamic effect and squeezing effect adds up to approximately 20 to 30 percent of the whole supporting force,suggesting that the fluid film's hydrodynamic effect and squeezing effect should be taken into account.As concerns the water-lubricated gear-shaft/journal-bearing interface,simulation results suggest that the defomation of the fluid film,which is the same order of magnitude as the film height and should be accounted for,results in a decrease in the fluid film's carrying capacity.This thesis presents an approach for lowering the outlet flow ripple by applying a tandem internal gear pump consisting of two gear pairs with an index angle between them.Simulation results suggest that the tandem pump could lead to a decrease in the outlet flow ripple in comparinson with a single pump with the same displacement in a wide range of operating conditions.This thesis also presents an approach for improving the lubricating performance of the water-lubricated gear-shaft/journal-bearing interface by applying micro shapes to the gear shaft's surface.The micro shapes are in the shape of sinusoidal waves and are shown to be able to improve the water film's carrying capacity.Experiments were carried out on a self-designed water hydraulic internal gear pump using tap water and mineral oil as the working media.Experimental results indicate that the frequency of IGPs' outlet pressure ripple is the same with the meshing frequency of the internal gear pair,which results from the displacing action of the gear pair.Apart from that,the outlet pressure could exhibit some frequency characterized by the rotational frequency of the ring gear or the gear shaft,which is caused by the manufacture tolerance of the gear pair.Additionally,experimental results indicate that polyetheretherketone(PEEK)is suitable for the lubricating interfaces in water hydraulic internal gear pumps,and the lubricating performance is strongly influenced by the clearance between the lubricating interfaces,which is in agreement with the conclusions drawn by the proposed model.