Thesis for PhD in Technical Sciences by speciality 05.22.20 "Operation and maintenance of vehicles". – Odessa National Maritime University, Odessa, 2019
The thesis is devoted to improving the durability of the basic units of axial-piston hydraulic machines, the development of tools that can be applied in the context of operation and maintenance. The specifics of axial-piston pumps and motors have been reviewed, as well as their responsibility in operation both as power tools of various machines, and mechanisms of vehicles. The intention to increase their reliability together with the urgent need to explain and solve the existing problems leads us to the conclusion that the line of research is of immediate interest.
The paper identifies the main causes for failures of units and parts of axial-piston hydraulic machines, and the overall impact on their longevity. The study of wear and leakage of cylinder block sets of axial-piston hydraulic machines has been conducted. A complex character of wear of these sets has been demonstrated, and the influence of their taper, hours of operation on leaks, depending on the cross-sections along the length of the piston or its position in the cylinder has been identified. The wear plots and patterns of the lubricant receipt along the length of the pistons have been received. For the first time it has been established theoretically and experimentally that by creating small longitudinal and ring microgrooves on the piston, it becomes possible to improve lubrication conditions, thus increasing the wear resistance of cylinder-piston pairs.
The analysis of the forces generated by the rotation of the cylinder block of axial-piston hydraulic machines has been conducted, which shows their uneven character depending on the passage of the cylinder bores above the valve plate slots. In the delivery port the valve plate clamping force is the greatest, which leads to its increased wear. The machine schematic has been developed that allows for strengthening through abrasive grinding of the spherical surfaces of valve plate of axial-piston hydraulic machines.
To enhance durability of parts of the axial-piston hydraulic machines it is proposed to use the electrophysical method of strengthening – an electromagnetic treatment. A number of practical recommendations for the appointment of strengthening modes has been developed: field strength, its variability, duration, time of exposure after the termination that can be used in manufacturing. It has been established that the durability of the spherical supports of connecting rods and pistons of hydraulic machines can be increased up to several times depending on the selected scheme of the electromagnetic effect. The paper proposes at first a combined treatment of the valve plate by magnetic hardening with the application of a copper film through selective transfer with the leveling of hydrogen influence, which can increase the durability of friction pairs several times. It has been established that the transmission of electromagnetic field in dynamic conditions via antifriction bearings increases their wear resistance and fatigue strength up to several times. However, it is necessary to clearly determine the modes of strengthening, since it is possible to obtain a negative effect as well. Summary data showing the relationship of the pendulum hardness, hydrogen evolution and durability (wear resistance) for all tested pairs of sliding friction and rolling of axial-piston hydraulic machines have been presented in relative units. The step-up ratio of durability is in the range of 1.2 - 2.5 times 30 hours after the termination of magnetic effect, and 1.5 - 2.8 times 100 hours after it. A particularly high effect – up to 8 times – has been noticed for ball bearings with the use of combined hardening treatment.
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The reliability of experimental data was ensured by using modern measuring complexes and high precision of measuring instruments (the maximum error by the experimental results did not exceed 5 %). The reliability of the obtained scientific results was achieved by repetition of the experiments using the factorial method of planning and statistical methods of analysis and observations processing under Student's t-test, two-factor analysis of variance and the Latin square of the first order.
Key words: strengthening, magnetic treatment, wear, leaks, hydrogen influence, reliability, grinding, white layers, taper ratio, durability, pistons, hydraulic machine, friction-electric method.
