The Shaft Torque of a Tandem Axial-Piston Pump

The objective of this study is to identify the best indexed position of two rotating groups within a tandem axial-piston pump for attenuating the torque ripple amplitude that is exerted on the shaft. By attenuating the torque ripple characteristics of the pump, other vibration aspects of the machine are also expected to be reduced. In particular, the objectives of this paper are aimed at reducing the noise that is generated by the pump. This paper begins by considering the theoretical torque ripple that is created by the discrete pumping elements of a single rotating group within an axial piston machine. From this analysis, an equation is produced that describes a single pulse for the torque ripple as a function of the average torque and the total number of pistons that are used within the rotating group. By superposing another rotating group on top of the first, and by indexing the angular position of one rotating group relative to the other, a second equation is produced for describing the theoretical torque ripple of a tandem pump design. This equation is also a function of the average shaft torque and the total number of pistons that are used within a single rotating group; however, an additional parameter known as the index angle also appears in this result. This index angle is shown to amplify or attenuate the amplitude of the torque ripple depending upon its value. From these results, it is shown that a proper selection of the index angle can reduce the torque ripple amplitude by as much as 75%.