Abstract:A novel virtual prototyping algorithm has been developed to design one of the most critical lubricating interfaces in axial piston machines of the swash plate type—the piston–cylinder interface—for operation with water as the working fluid. Due to its low viscosity, the use of water as a lubricant can cause solid friction and wear in these machines at challenging operating conditions. The prototyping algorithm compensates for this by tailoring the shape of the bore surface that guides the motion of each piston… Show more
“…22 More information on this model and its validation is available in, 23,24,14,25,5,26 and an example of the design of water-lubricated piston–cylinder interfaces in a commercial APMSPD using the model, with physical testing, can be found in. 27 Since its outputs serve as performance markers in the design studies to follow, a brief overview of the model will be provided here, guided by Figure 5.Figure 5.Multi-physics lubricating interface model (image based on Ref. 20).…”
Water’s low viscosity renders it a poor lubricant, but its green footprint, non-toxicity, inflammability, and low cost make it a desirable hydraulic fluid. Axial piston machines running on water are commercially available, but, especially the larger units, do not operate in the high-pressure regime ( ≥300 bar). The present work investigates micro surface shaping as a design solution for the critical piston–cylinder interfaces of these units, which are particularly hard-struck by the low viscosity of water in that the pistons are subject to a heavy side load, and these interfaces cannot be hydrostatically balanced. Through virtual prototyping, the effect of two surface shapes at a high-pressure operating condition is studied for the case of a 75 cc commercial unit: first, the concave bore profile, which gives the bore surfaces through which the pistons travel the lengthwise cross-section of a circular arc, and second, the barrel piston profile, which bestows this cross-section on the piston running surface instead. The design studies conducted show that, on account of the manner in which the pistons of these machines deform over the high-pressure stroke, the concave bore profile is most able to improve overall load support when its apex is in the middle of the guide length, or shifted toward the displacement chamber. Furthermore, the concave bore profile outperforms the barrel piston profile, largely because when the piston’s axial movement takes its apex into the displacement chamber, this surface shape is no longer able to enhance the piston-bore surface conformity at the end of the interface bordering the displacement chamber that is conducive to hydrodynamic pressure buildup in that region.
“…22 More information on this model and its validation is available in, 23,24,14,25,5,26 and an example of the design of water-lubricated piston–cylinder interfaces in a commercial APMSPD using the model, with physical testing, can be found in. 27 Since its outputs serve as performance markers in the design studies to follow, a brief overview of the model will be provided here, guided by Figure 5.Figure 5.Multi-physics lubricating interface model (image based on Ref. 20).…”
Water’s low viscosity renders it a poor lubricant, but its green footprint, non-toxicity, inflammability, and low cost make it a desirable hydraulic fluid. Axial piston machines running on water are commercially available, but, especially the larger units, do not operate in the high-pressure regime ( ≥300 bar). The present work investigates micro surface shaping as a design solution for the critical piston–cylinder interfaces of these units, which are particularly hard-struck by the low viscosity of water in that the pistons are subject to a heavy side load, and these interfaces cannot be hydrostatically balanced. Through virtual prototyping, the effect of two surface shapes at a high-pressure operating condition is studied for the case of a 75 cc commercial unit: first, the concave bore profile, which gives the bore surfaces through which the pistons travel the lengthwise cross-section of a circular arc, and second, the barrel piston profile, which bestows this cross-section on the piston running surface instead. The design studies conducted show that, on account of the manner in which the pistons of these machines deform over the high-pressure stroke, the concave bore profile is most able to improve overall load support when its apex is in the middle of the guide length, or shifted toward the displacement chamber. Furthermore, the concave bore profile outperforms the barrel piston profile, largely because when the piston’s axial movement takes its apex into the displacement chamber, this surface shape is no longer able to enhance the piston-bore surface conformity at the end of the interface bordering the displacement chamber that is conducive to hydrodynamic pressure buildup in that region.
“…The design of lubricating interfaces of these machines is a critical aspect of designing efficient axial piston machines [4]. Among the three lubricating interfaces of an axial piston machine, the piston/cylinder interface is by far the most critical interface in determining the efficiency and operating limits of the machine [2] owing to its completely hydrodynamic nature. Especially when using water as the working fluid, the design of these interfaces becomes more challenging owing to the physical properties of water.…”
Axial piston machines find their use over a wide range of the power spectrum owing to their superior reliability, efficiency, and power density. They are also a key component in applications like reverse osmosis and firefighting wherein the working fluid is water. Utilizing low viscous fluid, such as water, as a working fluid poses challenges in designing the critical lubricating interfaces of the piston pumps. Specifically, low viscosity makes it difficult for the lubricating interfaces to provide sufficient bearing and sealing functions in challenging operating conditions. In order to maintain the lubricating interface performance in water hydraulic piston pumps, costly materials, and tight manufacturing tolerances are often utilized. To improve the efficiency and cost-effectiveness of these pumps, accurate numerical simulation tools that consider the fluid and structure interaction are needed to provide valuable insights into these lubricating interfaces. Although the Reynolds equation is a reliable method for determining the fluid pressure distribution in an oil-based piston pump, it assumes a laminar flow which may not be applicable to water piston machines. For example, in an inclined piston/cylinder interface of a water hydraulic pump, there may be regions in the film wherein the large gap height combined with the low viscosity of water induce turbulence effects. If the traditional Reynolds equation is used in such a scenario, it is likely to overestimate the leakage flow through the interface as it does not account for turbulence. Therefore, it is important to incorporate the effect of turbulence in the diffusive terms of the Reynolds equation to accurately describe the Poiseuille flow with high Reynolds numbers. The challenge is further compounded by the micromotion and deformation of the solid body, resulting in the unevenness of the gap height in the lubricating film. Therefore, the consideration of turbulence can only be applied regionally in such cases. The current study proposes a fluid-structure interaction model with the consideration of the localized turbulent effects. This modeling approach is applied to the piston/cylinder interface of an axial piston machine that uses water as the working fluid. The approach stems from the modification of the Poiseuille term to incorporate a function of the Reynolds number. The fluid dynamics considering the turbulence effect was validated against the solution of the Navier Stokes equation using commercial CFD software. The modified Reynold equation was implemented in an axial piston pump EHL model coupled with the multi-body dynamics. The simulation results from the novel pump model were compared to a measurement and the accuracy of the proposed model was found largely improved from the traditional laminar solution. The calculated flow rate was found to be 54.6% lower with the additional consideration of the turbulence effect in the studied case.
“…Water has low viscosity, so the use of water as a lubricant can cause solid friction and wear in water hydraulic axial piston pumps under challenging operating conditions [1]. The testing of a physical prototype over a range of different operating conditions showed significant wear on the bores, indicating that the grooves in the pistons of this unit, which are likely to be responsible for much of this wear, should be removed.…”
Water hydraulic components and systems play pivotal roles in the development of modern hydraulics. Sustainable development and environmental protection cannot be imagined without the use of water as a working medium in modern hydraulic systems. An axial piston pump is the main component of these systems. This paper presents analytical and experimental methods for the development of an axial piston pump. The presented mathematical model is rooted in numerous research results in the literature and in our own experience. It is based on mathematical modelling of hydrodynamic processes of a water hydraulic axial piston pump which, combined with experimental research, provides a great tool to analyse the influence of different factors on the operating process and to optimise the pump parameters. The experimental equipment used in our tests simulates a real hydraulic installation, and the obtained results are very close to the actual operating parameters. This research included a modification of the swash plate in order to achieve ideal operating parameters and, thus, extend the service life of the pump. Water has a number of advantages over conventional hydraulic oils. It is a sustainable, environmentally friendly resource, more readily available than oil (lower transportation costs), cheaper to dispose of, non-flammable and non-toxic, and its high thermal conductivity aids in cooling.
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