Modelling and validation of a roller-cam rail mechanism used in a 2D piston pump

Abstract

The 2D principle is a new concept in hydrostatic pump design. It features a piston with a compound motion of both rotation and reciprocation to realize the functions of pumping and distribution. The compound motion is achieved through a specially designed roller-cam rail mechanism. Compared with conventional axial piston pumps, the 2D pump avoids sliding friction pairs completely and optimizes the force balanced conditions in the pump, making it easier to operate at the condition of higher speeds. The pump is also highly integrated for four cycles of suction and delivery for each round of the piston and thus has increased power density. Additionally, by applying a pair of pump units in tandem, the pump eliminates the structural flow ripple, caused by the limited number of pump elements, which exists in traditional pumps. The performance of the proposed 2D pump is highly dependent upon the motion conversion mechanism, especially the roller-cam rail mechanism. A mathematical model of the cam rail is developed and compared with its experimental counterpart to demonstrate its precision. Then, the performance of the piston and the no-load flow characteristics of the tandem pump are tested and analyzed to show the effectiveness of the roller-cam rail mechanism and the viability of the tandem pump. Although the curves of no-load flow characteristic of the tandem pump include a lot of clutter, by analyzing the frequency spectrogram of the curves of flow and revolving speed, they can be smoothed by applying a band-pass filter to remove that clutter. For comparison, the flow ripple in the experimental and simulation results of the tandem pump is smaller than that in simulation results of the traditional piston pump at low pressure. Both the theoretical analysis and experimental results indicate that the surface of the cam rail is precise and the pump has the potential advantage of eliminating sliding friction pairs and flow ripple.