Volumetric flow pulsations of piston pumps lead to pressure fluctuations within hydraulic systems. A secondary swash plate angle, known as cross angle, has been used in the past to reduce pulsations with great success. However, research in this field has been scarce for the last two decades. In the proposed paper, a 9-piston pump is investigated to determine the effects of the cross angle on commutation, acting forces and torques as well as volumetric flow and pressure pulsations. This contribution presents a detailed description of the piston kinematics, the simulation model used and the subsequent simulation results. In addition, an experimental validation strategy is proposed.As a secondary swash plate angle leads to a different mathematical function for the piston stroke compared to a pump without cross angle, a kinematic model for the piston movement was derived using linear transformations between three coordinate systems. The changed kinematics of the pump result in an increase in piston stroke as well as in an angular phase shift of the bottom and top dead centre coordinates, which is primary swash plate angle dependent. Consequently, variable commutation between the pistons and both kidneys of the port plate are achieved by using a cross angle.To examine the overall impact of a secondary swash plate angle on an axial piston pump, a simulation model was constructed and parameter variations were conducted. The results show a significant effect of the cross angle on overall pump performance. One of the observations is a notable reduction in high-pressure backflow and a minor increase in low-pressure backflow during commutation over the complete range of the primary swash plate angle. This leads to smaller energy losses associated with the high-pressure backflow and increased energy losses associated with the low-pressure backflow. However, the latter are much smaller compared to the former and consequently overall energy losses are reduced.It was also observed that the changed kinematics of the pump affect the forces and torques acting on the swash plate. Although a piston force of greater magnitude was noted, it was observed that the overall torque generated by the individual pistons was actually reduced. The cause of this is a change in the lever arms of the piston forces acting on the swash plate. This leads to a significant reduction in required control force and torque acting on the swash plate and opens the prospect of energy saving and cost reduction via control actuator optimization.The simulation results also reaffirm that the cross angle is a viable concept to reduce volumetric flow and pressure pulsations. It was found that the pulsations are generally smaller over a wide range of operating conditions compared to a pump without cross angle. This is especially the case at very small swash plate angles, where a significant reduction in the flow ripple was achieved. This is attributed to the longer pre-compression phase resulting from the changed piston kinematics.All in all, the investigations presented in this contributions indicate, that the cross angel is a promising concept for reducing volumetric flow and pressure pulsations, acting forces and torques as well as energy losses. The simulative investigations and proposed validation strategy can serve as a foundation for further exploring the potential of this concept.

Modelling of the Cross Angle and its Impact on Pump Performance

Paper Proceedings: https://asmedigitalcollection.asme.org/FPST/FPMC2021/volume/85239

2021 ASME/BATH Symposium on Fluid Power and Motion Control (FPMC2021)

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