This paper first introduces the structure and working principle of a 2D piston pump invented by the research team that the authors are involved with. Afterward, the mechanism of the churning losses caused by the pump's moving parts, which are rotating in oil, is carefully studied by building up mathematical models and using CFD simulations. A test rig is set up to estimate the churning losses of the moving parts by monitoring the torque at different rotational speeds. The analytical results indicated that the torque of the churning losses increased with the increase of the rotational speed. In addition, the experimental data of the churning losses were consistent with the solutions from both the conducted mathematical models and CFD simulations before the rotational speed reached 8000 rpm. However, when the rotational speed exceeded 8000 rpm, the experimental data showed an apparent difference from the calculated ones. Based on the changes in the oil temperature and noise, this difference might be due to cavitation or turbulence. As a result, the churning losses that took place in the 2D high-speed piston pump need to be further studied, especially when the pump is driven by a high-speed motor.

Since many studies on axial piston pumps aim at enhancing their high power-weight ratio, many researchers have focused on the generated mechanical losses by the three friction pairs in such pumps and attempted to diminish them through abundant and new structural designs of the pump’s components. In this paper, a high-speed 2D piston pump is introduced and its architecture is specifically described. Afterward, a mathematical model is established to study the pump’s mechanical efficiency, including the mechanical losses caused by the viscosity and stirring oil. Additionally, in this study the influences of the rotational speed, the different load pressures, and the rolling friction coefficient between the cone roller and the guiding rail are considered and discussed. By building a test rig, a series of experiments were carried out to prove that the mechanical efficiency was accurately predicted by this model at low load pressures. However, there was an increasing difference between the test results and the analytical outcomes at high pressures. Nevertheless, it is still reasonable to conclude that the rolling friction coefficient changes as the load pressure increases, which leads to a major decrease in the mechanical efficiency in experiments.

Axial piston pumps with high rotational speeds are required in many fields to increase the power-to-weight ratio. However, three main sliding friction pairs in the pump restrict the increase in rotational speed. To solve this problem, we propose a 2D piston pump with a balanced force that contains a sliding friction pair. Firstly, the mechanical structure and working principle of the pump are described. Then, the pump volumetric efficiency is studied by mathematical modeling, and volumetric losses containing backflow and leakage are analyzed and discussed from the perspectives of load pressure and rotational speed. A test bench that verifies the mathematical model is built to measure the volumetric efficiency of the tested pump. We have found that the increase in rotational speed can help to increase the pump volumetric efficiency, and the mathematical model is consistent with the tested data for 1000 rpm but demonstrates a remarkable difference from the tested data for 3000 rpm. Thus, the temperature field of the pump and the viscosity-temperature characteristics of the oil must be taken into account to increase volumetric efficiency further.

Flowmeters play a critical role in hydraulic systems. Following a review of positive displacement flowmeters, we hereby introduce a novel positive displacement flowmeter with parallel twodimensional pistons as metering units. The working principle involves simultaneously utilizing both the rotational and reciprocation movements of a two-dimensional piston and paralleling two two-dimensional pistons to prevent flow rate fluctuations. Consequently, we established a mathematical model to describe the cam track curves and the displacement of the flowmeter. Meanwhile, the pressure loss is analyzed and the leakage flow rate is estimated to compensate the relative error. Finally, we designed and fabricated a prototype to measure the flow rate with ranges of 1-25 L/min. The experimental results show that the prototype has a reading uncertainty of less than 2%, a linearity of around ±3.8% and relative errors of less than ±2.9%. The pressure loss for the prototype increases linearly with the total flow rate and reaches 3 bar at 25 L/min. These characteristics are acceptable considering that this prototype is the first set of two-dimensional piston flowmeters. The shortcomings of this first-generation flowmeter are discussed in the conclusion part to provide guidance to enhance the performance of next-generation prototypes. INDEX TERMS Fluid power, hydraulic system, hydraulic component, flowmeter, two-dimensional piston.

No abstract