Integrated slipper retainer mechanism to eliminate slipper wear in high-speed axial piston pumps

Abstract

The power density of axial piston pumps can greatly benefit from increasing the speed level. However, traditional slippers in axial piston pumps are exposed to continuous sliding on the swash plate, suffering from serious wear at high rotational speeds. Therefore, this paper presents a new integrated slipper retainer mechanism for high-speed axial piston pumps, which can avoid direct contact between the slippers and the swash plate and thereby eliminate slipper wear under severe operating conditions. A lubrication model was developed for this specific slipper retainer mechanism, and experiments were carried out on a pump prototype operating at high rotational speed up to 10000 r/min. Experimental results qualitatively validated the theoretical model and confirmed the effectiveness of the new slipper design.

Graphical abstract

Keywords

axial piston pump / high speed / slipper wear / slipper design / retainer / lubrication model

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Nomenclature

Abbreviations
BDC	Bottom dead center
DLC	Diamond-like carbon
DLC + WC	W-doped DLC coating
HP	High-pressure
LP	Low-pressure
Variables
ap	Acceleration of the piston along its centerline
fb	Friction coefficient between the piston ball and slipper socket
fp	Friction coefficient between the piston and cylinder bore
Fa	Reciprocating inertial force of the piston-slipper assembly
Fb	Contact force between the piston ball and slipper socket
Fd	Pressure force from the displacement chamber
Ff	Friction force between the piston and cylinder bore
Fs	Spring force exerted by the spherical cup
Fc	Total clamping force
Fh	Separating force generated by the fluid film
h	Gap height
h1, h2, h3	Gap heights at three points
hmax	Maximum gap height
hmin	Minimum gap height
Jp	Piston’s moment of inertia about its axis
l	Contact length of the piston within the cylinder bore
l0	Initial contact length of the first piston
L	Piston length
m	Mass of one piston-slipper assembly
mp	Piston mass
Mx	Moment component of Mc in the x direction
My	Moment component of Mc in the y direction
Mc	Moment generated by the total clamping force
Mh	Moment generated by the separating force
N1, N2	Contact forces between the piston and cylinder bore at two engaging ends
p	Fluid pressure
pc	Casing pressure of the pump
p(φi)	ith displacement chamber pressure as a function of the angular displacement
r	Radial distance from the coordinate origin
rb	Piston ball radius
rp	Piston radius
R	Pitch radius of the kidney-shaped pockets in the sliding plate
R1	Inner radius of internal sealing land

R2	Outer radius of internal sealing land
R3	Inner radius of external sealing land
R4	Outer radius of external sealing land
Rp	Piston pitch radius
t	Time
vp	Velocity of the piston along its centerline
Vp	Resultant velocity of the piston relative to the cylinder block
α	Angular span of the kidney-shaped pocket in the sliding plate
β	Swash-plate angle
θ	Angular distance from the y axis
θa	Azimuth angle of the minimum or maximum gap height
φ	Angular displacement of the piston from the BDC
μ	Fluid dynamic viscosity
ρ	Fluid density
\omega	Rotational speed of the pump
{\omega }_{\mathrm{p}}	Spinning speed of the piston
{\omega }_{\mathrm{s}}	Rotational speed of the sliding plate

Acknowledgements

This work was supported by the National Key R&D Program of China (Grant No. 2019YFB2004504), the National Natural Science Foundation of China (Grant No. 52005323), the National Outstanding Youth Science Foundation of China (Grant No. 51922093), the China National Postdoctoral Program for Innovative Talents (Grant No. BX20200210), and the China Postdoctoral Science Foundation (Grant No. 2019M660086). The authors are thankful to research fellow Wunong Hu and senior engineer Yan Zhang, both at AVIC Xi’an Flight Automatic Control Research Institute, for their kind help during tests on the high-speed axial piston pump prototype.

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2022 Higher Education Press 2022.