Research On Some Key Technologies Of High-Speed Rotation For Axial Piston Pumps Used In EHAs

In aerospace applications,the axial piston pump is one of key components for the electro-hydrostatic actuator(EHA),which is characterized as small size and high power density.It is an effective way to reduce the size and improve the power density of EHA pumps by increasing their rotational speed.However,high-speed operating conditions can lead to several challenges for the pump design,including the slipper wear,cylinder block tilt and displacement chamber cavitation.This dissertation focused on the above challenges and explored novel structures and design criteria for the rotating group of the EHA pump.The research results have provided valuable guidance for the fabrication of the EHA pump prototype.The main contents of this dissertation are as follows(1)The working principle of traditional distributed slippers was introduced and their oil film thickness was measured over one cycle under real operating conditions.The analysis results provided critical insight into the potential challenges that the traditional slippers face under extreme conditions.A novel integrated slipper was designed to eliminate the wear of traditional slippers,followed by the developed lubrication model to predict its lubrication characteristics.The wear conditions between the two types of slippers were compared under high speed and high pressure conditions,which confirmed the advantages of the novel integrated slipper and validated its lubrication model.(2)The effects of the piston-slipper assemblies' inertia forces on the cylinder block tilt were studied theoretically and experimentally.To avoid serious cylinder block tilt at high speed,the design criterion for the cylinder block spline was derived,and it was verified by existing data coming from actual products.To reduce the heat generation of EHA motor,a load-sensing mechanism was proposed for the EHA pump and its actual p-V curve was investigated under the influence of the piston-slipper assemblies'inertia forces.The experimental results for the EHA pump and system prototypes verified the proposed load-sensing mechanism.(3)A theoretical analysis was performed to evaluate the sensitivity of the cylinder block tilt to the manufacturing errors of the rotating group.Some typical manufacturing error criteria were derived based on the operating conditions and allowable tilting moment acting on the cylinder block.The presented criteria were verified by the experimental campaigns for different levels of manufacturing errors.They provided specific guidance for the design,fabrication and assembly of the EHA pump's rotating group.(4)Analytical and CFD simulation models were developed to predict the displacement chamber pressure and cavitation.A full cavitation model was created to reveal the centrifugal effects on the pressure distribution and cavitation in the displacement chambers.To reduce the gaseous cavitation,an inward-inclined design was proposed for the cylinder ports,which took advantage of the centrifugal effect to push the rotating fluid at the cylinder ports into the displacement chambers.As a result,the improved suction performance increased the effective delivery flow rate of the EHA pump at high speed.