Wear Mechanisms in Contacts Involving Slippers in Axial Piston Pumps: A Multi-Technical Analysis
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JMEPEG https://doi.org/10.1007/s11665-018-3610-5
Wear Mechanisms in Contacts Involving Slippers in Axial Piston Pumps: A Multi-Technical Analysis G. Schuhler, A. Jourani, S. Bouvier, and J.-M. Perrochat (Submitted October 20, 2017; in revised form June 8, 2018) Axial piston pumps are widely used in actuation as power conversion systems, especially in aeronautics. Even though they combine compactness and efficiency, wear of their parts reduces their lifespan. Studies on these pumps often consist in analytic or numerical analyses of lubricated contact between their components. Piston slippers are in tribological contacts with swashplate, pistons and slipper retainer. This study aims to understand wear mechanisms in the contacts involving this central component. An experimental multitechnical analysis of helicopter pumps parts after several functioning times is presented. To determine wear mechanisms, worn surfaces are observed with SEM. 3D surface roughness measurements provide surface topography. Contact conditions and consequently wear severity and mechanisms differ from one contact to another. Detached coarse carbides from the swashplate surface act as an abrading third-body against slippers and swashplate. Debris generated in this contact is carried by the fluid to the other contacts. Although pistons are made of the same steel as swashplate, there is no carbide detachment and wear comes from debris polluting the fluid. Slipper retainer is almost not worn, and debris causes abrasive wear and craters generation in the slippers. Keywords
axial piston pump, boundary lubrication, carbide, microstructure, stainless steel, wear mechanisms
1. Introduction Axial piston pumps are used to put a fluid into motion in hydraulic circuitries. They are activated by a motor rotation which is transmitted to the pump barrel. In the barrel, pistons are held on the swashplate. The swashplate is a tilted plate that forces the pistons to translate in the rotating barrel. These translations result in a fluid pumping. The fluid is then distributed between the inlet and the outlet by the valve plate. By creating a contact between nominally flat surfaces, piston slippers (or slippers) improve sliding between pistons and the swashplate. In this study, a plate is pushed by a spring in order to maintain slippers held against the swashplate. This plate will be designated as slipper retainer (Fig. 1). The pump housing is filled with hydraulic fluid, which also acts as a lubricant. A cavity in the pistons and slippers lets a small amount of pressurized fluid out of the barrel. Thus, the contact between slippers and pistons and especially slippers and swashplate are better lubricated. The most simulated or experimentally studied contact in the literature is slipper/ swashplate and its lubricating film (Ref 1-8). G. Schuhler, Sorbonne University, Universite´ de technologie de Compie`gne, FRE UTC-CNRS 2012 Roberval, Centre de recherche Royallieu, CS 60 319, 60 203 Compie`gne Cedex, France; and Interiors, Actuation and Propeller Systems, UTC AEROSPACE SYSTE
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