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Research Papers

Analyses of the Long-Term Performance and Tribological Behavior of an Axial Piston Pump Using Diamondlike-Carbon-Coated Piston Shoes and Biodegradable Oil

[+] Author and Article Information
M. Kalin

Centre for Tribology and Technical Diagnostics, University of Ljubljana, Bogisiceva 8, 1000 Ljubljana, Sloveniamitjan.kalin@ctd.uni-lj.si

F. Majdič, J. Vižintin, J. Pezdirnik, I. Velkavrh

Centre for Tribology and Technical Diagnostics, University of Ljubljana, Bogisiceva 8, 1000 Ljubljana, Slovenia

J. Tribol 130(1), 011013 (Dec 26, 2007) (8 pages) doi:10.1115/1.2805442 History: Received March 06, 2007; Revised August 14, 2007; Published December 26, 2007

This work reports on the performance enhancement of a real-scale hydraulic system consisting of diamondlike-carbon (DLC)-coated components in combination with biodegradable oil in long-term experiments under conditions simulating those in an actual application. The performance of a hydraulic axial piston pump with DLC-coated piston shoes was evaluated in a newly designed, dedicated hydraulic test system using fully formulated biodegradable, synthetic ester oil. For comparison, an equal but separated hydraulic system with a conventional commercial pump and stainless-steel shoe surfaces was tested. The tests were run at 85% of the maximum pump load and an oil temperature of around 80°C for a period of 2000h, which corresponds to more than 1yr of continuous 8hday operation in an application. A major abrupt oxidation-induced degradation of the oil did not occur in either system; however, the oil from the system comprising the DLC-coated shoes showed noticeably and consistently better results. The wear of the DLC-coated shoes, especially during the running in, was much lower than that in the conventional steel system. Only minor polishing wear was observed on the DLC shoe’s sliding surfaces during the test period, while on the steel shoe’s surfaces, many scratches were found and some erosion of the edges was detected.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 3

Assembly of the pistons with DLC-coated shoes, inserted into the pump cylinder block

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Figure 4

(a) A photograph of the hydraulic piston-pump test rig with two identical testing systems and (b) schematic of a single hydraulic circuit (positions: 1.0, variable axial piston pump); 2.0, electric motor; 3.0, relief valve; 4.0, pressure-compensated flow-control valve; 5.0, water cooler; 6.0, return-line filter with pressure indicator and bypass valve; the ß value for a particle size over 25μm is more than 150 (absolute filtration at that size); 7.0, pressure gauge; 8.1 and 8.2, microhose coupling; 9.0, reservoir 30l

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Figure 5

Wear loss of the set of conventional and DLC-coated shoes

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Figure 6

A photograph of the piston-shoe front surfaces after 500h on (a) DLC-coated piston shoe and (b) steel piston shoe

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Figure 7

A photograph of the piston-shoe front surfaces after 750h on (a) DLC-coated piston shoe and (b) steel piston shoe

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Figure 8

A photograph of the piston-shoe front surfaces after 2000h on (a) DLC-coated piston shoe and (b) steel piston shoe

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Figure 1

Typical triglyceride composition (vegetable oil) with three different types of fatty acid having different levels of saturation (number of double bonds)

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Figure 2

Schematic of the design and the working principle of the axial piston pump

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Figure 9

Leakage of the oil in the pump with the conventional steel and DLC-coated shoes, compared to the initial/inherent pump leakage

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Figure 10

Kinematic viscosity of the oil in the systems with conventional and DLC-coated piston-shoe surfaces during the 2000h test

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Figure 11

TAN measurements of the oil for conventional steel and DLC-coated piston-shoe surfaces during the 2000h test

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