Hydraulic piston pump in civil aircraft: Current status, future directions and critical technologies

The piston-cylinder pair is the key friction pairs in the piston pump. Its performance determines the volume efficiency of piston pump. With the increase of load pressure, the leakage at the clearance of piston-cylinder pair will also increase. In order to reduce leakage, the clearance of the piston-cylinder pair of the ultra-high pressure piston pump is smaller than that of the medium-high pressure piston pump. In order to explore whether the piston will stuck in the narrow gap, it is necessary to study the oil film characteristics of the piston-cylinder pair under the condition of ultra-high pressure, so as to provide a theoretical basis for the optimal design of the piston-cylinder pair of ultra-high pressure axial piston pump. In this paper, an ultra-high pressure axial piston pump is taken as the research object, and its structural characteristics are analyzed. The mathematical model of the oil film thickness of the piston-cylinder pair is established by using the cosine theorem in the cross section of the piston. The finite volume method is used to discretize the Reynolds equation of the oil film of the piston-cylinder pair, and the over relaxation iteration method is used to solve the discrete equations, and the mathematical model of the oil film pressure of the piston-cylinder pair is obtained. The mathematical model of oil film thickness and pressure field of piston-cylinder pair is solved by programming. The dynamic change process of oil film thickness and pressure field of the plunger pair of the ultra-high pressure axial piston pump under the load of 20 MPa and 70 MPa is obtained. Under the two conditions, the thinnest area of the oil film reaches 3 μm and 2 μm dangerous area respectively; the oil film pressure reaches 20 MPa and 70 MPa respectively when the swashplate rotates 10° and continues to increase with the increase of swashplate rotation angle. When the rotation angle reaches 90°, the oil film pressure also reaches the maximum value, but there is no pressure spike phenomenon. The oil film pressure characteristics of ultra-high pressure axial piston pump under conventional and ultra-high pressure conditions were obtained by modification and experimentation.

Study on Oil Film Characteristics of Piston-Cylinder Pair of Ultra-High Pressure Axial Piston Pump

The equations of motion of a conventional piston in axial piston pumps and motors with metallic contacts are derived. For swash plate types, the fluid film shape between the piston and the cylinder wall, contact forces and loss of power are numerically obtained in relation to both the operating conditions and piston dimensions. The length of the sealing part composed of the piston and cylinder wall is, in particular, shown to considerably affect the loss of power. Finally, the validity of the analysis is discussed by comparison with the results of a performance test of a pump for high water content fluids.

Motion of the piston in piston pumps and motors: The case of metallic contact.

The authors propose a temperature adaptive piston design for axial piston machines of swash plate type. The proposed piston helps to keep the film thickness between piston and cylinder close to optimal with respect to energy dissipation while operating temperature can change in a wide range. The authors utilize the thermal deformation of piston and cylinder, which varies with temperature, to design the interface that adapt the gap height to compensate the change of the fluid viscosity with the temperature. An in-house developed fluid-structure and thermal interaction model together with recently developed port and case temperature prediction model are used to analyze the piston/cylinder interface and to predict resulting part temperatures, deformations, the fluid film properties and resulting energy dissipation, friction and leakage of the proposed novel design. The results show a reduction of energy dissipation over a large range of operating temperature for the proposed design compared to the ba...

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A temperature adaptive piston design for swash plate type axial piston machines

This paper outlines some of the developments in fluid power technology to overcome the challenges posed by other forms of energy transmission. It is shown that many of these advances are associated with the incorporation of electronic devices, microprocessors and the application of modern control techniques as well as improvements in fluid power components. A central issue is the reduction of pump flow-ripple in order to reduce system vibration and noise. Other environmental factors are also discussed.

Fluid Power-Progress in a Key Technology.

Assuming that a piston and a cylinder bore are geometrically cylindrical and that the reciprocating and rotational velocities of the piston are given, the motion of pistons for piston-type hydraulic machines is analyzed by perturbation method. It is shown that in general the motion of pistons is unstable. Hydraulic lock in spool valves is concluded to be fundamentally caused by the instability of the motion of spools (pistons). For the special case where the motion is stable, the effects of fluid pressure, the piston length, etc. on the radial displacement of pistons are numerically presented.

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Motion of Pistons in Piston-Type Hydraulic Machines : 1st. Report : Theoretical Analysis

In this report the results of test carried out with a rig modeled after a piston pump to varify the theoretical analysis are presented. The friction at the connecting-rod bearings is shown to affect the motion of the piston considerably. It is concluded that the calculated values including the friction coincide fairly well with the test results excepting the low rotational speed-case where the piston comes into contact with the cylinder wall.

Atsushi Yamaguchi

Papers

Motion of Pistons in Piston-Type Hydraulic Machines : 1st. Report : Theoretical Analysis

Motion of Pistons in Piston-Type Hydraulic Machines : 2nd. Report : Experiment