Research on the fluid film lubrication between the piston-cylinder interface

Abstract

The fluid film between piston and cylinder works simultaneously as bearing and lubricating functions, its thickness determines the lubrication efficiency and performance of an axial piston pump. Because of the thickness is usually micron level, and its change in the whole cycle is difficult to observe directly. In order to reveal it particularly, this paper present a mathematical model which considering structure, piston kinematics and a dynamic piston load to predict the film thickness in a cycle. The minimum thickness is used as an index to evaluate lubrication performance and its variation are studied under different load pressure, rotating speed and length ratio between cylinder and piston. A special test rig with four displacement sensors placed through the cylinder surface allows measuring the film thickness at these points. The model was verified by comparing the numerical results with measurements taken on the test rig. Results indicate that: (1) The mathematical model could effectively predict the film thickness trend and the position of the minimum thickness; (2) The minimum thickness in pressure phase is greater than in suction phase, and increases with the increase of load pressure and decreases with the increase of rotation speed, the influence of load pressure on film thickness is much greater than that of rotational speed. (3) Increasing the length ratio reduces the piston eccentric and raises the minimum film thickness, and in order to obtain the better lubrication, the length ratio should be greater than 0.5.

The Impact of the Deformation Phenomenon on the Process of Lubricating and Improving the Efficiency Between the Slipper and Swashplate in Axial Piston Machines

“…In FIGURE 2, F wKi is the centrifugal force, F RKi is the piston ball joint force, F DK is the displacement chamber force, F TKi is the force of the cylinder block, F aKi is the inertia force, F TG is the Slipper viscous friction force, (F SKyi , F SKzi ) are the components of swashplate reaction force, and F RK is the resultant of piston/slipper assembly force. These forces have been mathematically modelled and expressed in detail by Haidak et al [13], Wang et al [33].…”

A New Approach for Modeling Mixed Lubricated Piston-Cylinder Pairs of Variable Lengths in Swash-Plate Axial Piston Pumps

“…Due to its simple and compact structure, the swash-plate axial piston pump is widely used in hydraulic systems. As one of the fundamental tribo-pairs of piston pumps, the piston-cylinder interface heavily affects the survival and overall performance of the pump, not only because it plays a role in sealing and bearing, but also because it serves as the main source of friction and fluid leakage [ 1 , 2 ]. Moreover, under heavy load conditions, the lateral force from the swash plate can easily induce mixed lubrication between the piston and cylinder, which further increases power consumption and shortens the service life of the pump [ 3 ].…”

“…Sun et al [ 2 ] modeled the piston-cylinder interface with consideration of the adaptive eccentricity and the force balance of the piston. Wang et al [ 1 , 11 , 12 ] predicted the lubrication and leakage performances of variable-length piston-cylinder interfaces in a swash-plate axial piston pump, considering piston structure, piston kinematics and dynamic load. Nie et al [ 13 ] proposed an elasto-hydrodynamic lubrication model for the piston-cylinder interface in a seawater hydraulic axial piston pump.…”

Patterns formed in a thin film with spatially homogeneous and non-homogeneous Derjaguin disjoining pressure

“…Moreover, thin liquid films occur in many technological applications such as coatings [22] and lubricants (e.g. oil films which lubricate the piston in a car engine [41], drying paint layers [18] and in the manufacture of microelectronic devices [21]). For extensive reviews of thin-film flow see, for example, Oron et al [28] and Craster and Matar [10].…”