FATIGUE LIFE IMPROVEMENT OF THE ROLLER SWASHPLATE BEARING OF AN AXIAL SWASHPLATE TYPE PISTON PUMP

The roller swashplate bearing in hydraulic piston pumps is very unique in applications of roller element bearings. The main advantages of this type of bearings are low friction, very small difference between start torque and steady state torque, and no additional pressure source is required for their functioning. Therefore, better control performance and higher efficiency can be expected from piston pumps with roller swashplate bearings, compared with pumps with hydrostatic or plain ones. However, it is particularly challenging to design a roller swashplate bearing to meet the very demanding and widely varying load requirements for heavy duty off-highway machine operations, considering cost and pump size limitations. Quite different from most other roller bearing applications, a roller swashplate bearing for heavy duty hydraulic piston pumps is subject to (a) extremely high contact pressure between rollers and races due to high system pressure, (b) high frequency oscillating forces in three dimensions caused by the torque ripple and discharge pressure ripple inherent in pump rotating group, (c) very unfavorable local lubrication conditions when the pump is operated with no or little displacement change, and (d) sliding between rollers and races because of frequent sudden pump displacement changes. Based on the observed failure modes of bearings in this application, this paper discusses several measures to improve the fatigue life of the swashplate roller bearing for an axial swashplate type piston pump used in a heavy duty off-highway machine. Analyses, simulation results, and machine operation results are provided to show the effectiveness of the proposed measures. 1