Tribological study on hydrostatic slipper bearing with annular orifice damper for water hydraulic axial piston motor

Hydrostatic slipper bearing is an effective way to maintain a fluid film between slipper pad and swash plate that slide against each other, and thereby mitigate direct surface-to-surface contact in water hydraulic axial piston motor (WHAPM). The hydrostatic slipper bearing with an annular orifice damper is proposed, and the reaction force of the bearing in WHAPM is investigated. The effects from the friction within the cylinder bore, the dynamics of the piston, and the centrifugal force of the piston–slipper assembly are examined. The characteristic equation of the hydrostatic slipper bearing with an annular orifice damper is formulated, where the effects of various geometric parameters (e.g. damping length, supporting length, and clearance between the piston and the cylinder bore) are reflected. The relevant criterion for designing the hydrostatic slipper bearing can then be established. Results of the theoretical analyses indicate that (a) the friction coefficient, the swash plate angle, and the inertia and centrifugal loads (generated under a high motor rotating speed) would have significant influences on the reaction force; (b) an appropriate swash plate angle can help eliminate the fluctuation of the reaction force; (c) the load-carrying capacity of the hydrostatic slipper bearing is more sensitive to the damping length than to the supporting length of the piston; (d) a short damping length can help enhance the load-carrying capacity; (e) a small clearance between the piston and the cylinder bore would help improve the adaptive ability to the varying load for the hydrostatic slipper bearing, when clearance between the slipper pad and the swash plate ranges from 5 to 20μm. Experimental studies of the slipper pads sliding against the swash plates are conducted at a custom-manufactured test apparatus, given different material combinations and design methods. The experimental results indicate that the hydrostatic slipper bearing with an annular orifice damper would decrease the possibility of the severe wear between the slipper pad and the swash plate in comparison with the hydrostatic clamping ratio bearing in the WHAPM, and the CRA laser cladding (compared to the ZrO2·MgO-plasma-sprayed coating and the stainless steel 2Cr13) is a promising candidate as the tribo-material when sliding against composite materials in water lubrication system. The hydrostatic slipper bearing with an annular orifice damper has been successfully applied to a WHAPM developed at the Huazhong University Science and Technology. The result demonstrates that the developed bearing has a satisfactory tribolgical performance, and can be extended to the manufacture of water hydraulic axial piston pumps.