scholarly journals Tailoring the Bore Surfaces of Water Hydraulic Axial Piston Machines to Piston Tilt and Deformation

Energies ◽  
2020 ◽  
Vol 13 (22) ◽  
pp. 5997
Author(s):  
Meike Ernst ◽  
Andrea Vacca ◽  
Monika Ivantysynova ◽  
Georg Enevoldsen
Keyword(s):  
Experimental Testing ◽  
Hydrodynamic Pressure ◽  
Operating Conditions ◽  
Surface Shape ◽  
Working Fluid ◽  
Total Efficiency ◽  
Positive Displacement ◽  
Piston Cylinder ◽  
Low Viscosity ◽  
Axial Piston

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 in this type of positive displacement machine to conform with the piston surface, taking into account both the piston’s tilt and its deformation. Shaping these surfaces in this manner can render the interface more conducive to generating hydrodynamic pressure buildup that raises its load-carrying capacity. The present work first outlines the structure of the proposed algorithm, then presents a case study in which it is employed to design a bore surface shape for use with two prototypes, one virtual and one physical—both modified versions of a 444 cc commercial axial piston pump. Experimental testing of the physical prototype shows it to achieve a significantly higher maximum total efficiency than the stock unit.

Cylinder Bore Micro-Surface Shaping for High Pressure Axial Piston Machine Operation Using Water as Hydraulic Fluid

2017 ◽  
Author(s):  
Meike H. Ernst ◽  
Monika Ivantysynova
Keyword(s):  
High Pressure ◽  
High Pressures ◽  
High Heat ◽  
Surface Shape ◽  
Working Fluid ◽  
Hydraulic Fluid ◽  
Hydraulic Systems ◽  
Piston Cylinder ◽  
Axial Piston Machine ◽  
Axial Piston

Water as a working fluid in hydraulic systems: the benefits of this particular hydraulic fluid are both numerous and consequential, but its implementation remains nontrivial for certain key applications. One of these key applications is the axial piston machine of swashplate type, which counts among its selling points efficiency, the possibility of variable displacement, and the ability to function in high-pressure systems [1]. Water as a working fluid tends to mar that last point with its extremely low viscosity — and the high leakages and low load support that stand as effects of that fluid property in the context of tribological interfaces. However, water’s environmentally friendly, fire resistant nature is coupled with a high thermal conductivity and high heat capacity favorable for keeping hydraulic systems cool, as well as a high bulk modulus that cuts slack in the exact execution of machine motions [2]. That makes it worth implementing in hydraulic systems, even in the face of the aforementioned troubles. This paper investigates the effects of a surface shape that can be applied to the cylinder bores of axial piston machines with the goal of improving load support while keeping down leakage in the critical piston cylinder tribological interface of axial piston machines operating at high pressures with water as their hydraulic fluid.

Heat Transfer and Thermal Elastic Deformation Analysis on the Piston/Cylinder Interface of Axial Piston Machines

2012 ◽  
Vol 134 (4) ◽  
Author(s):  
Matteo Pelosi ◽  
Monika Ivantysynova
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Elastic Deformation ◽  
Hydrodynamic Lubrication ◽  
Operating Conditions ◽  
Fluid Film ◽  
Design Elements ◽  
Piston Cylinder ◽  
Viscous Shear ◽  
Axial Piston

The piston/cylinder interface of swash plate–type axial piston machines represents one of the most critical design elements for this type of pump and motor. Oscillating pressures and inertia forces acting on the piston lead to its micro-motion, which generates an oscillating fluid film with a dynamically changing pressure distribution. Operating under oscillating high load conditions, the fluid film between the piston and cylinder has simultaneously to bear the external load and to seal the high pressure regions of the machine. The fluid film interface physical behavior is characterized by an elasto-hydrodynamic lubrication regime. Additionally, the piston reciprocating motion causes fluid film viscous shear, which contributes to a significant heat generation. Therefore, to fully comprehend the piston/cylinder interface fluid film behavior, the influences of heat transfer to the solid boundaries and the consequent solid boundaries’ thermal elastic deformation cannot be neglected. In fact, the mechanical bodies’ complex temperature distribution represents the boundary for nonisothermal fluid film flow calculations. Furthermore, the solids-induced thermal elastic deformation directly affects the fluid film thickness. To analyze the piston/cylinder interface behavior, considering the fluid-structure interaction and thermal problems, the authors developed a fully coupled simulation model. The algorithm couples different numerical domains and techniques to consider all the described physical phenomena. In this paper, the authors present in detail the computational approach implemented to study the heat transfer and thermal elastic deformation phenomena. Simulation results for the piston/cylinder interface of an existing hydrostatic unit are discussed, considering different operating conditions and focusing on the influence of the thermal aspect. Model validation is provided, comparing fluid film boundary temperature distribution predictions with measurements taken on a special test bench.

Maximum Power From Fluid Flow by Applying the First and Second Laws of Thermodynamics

2016 ◽  
Vol 139 (3) ◽  
Author(s):  
German Amador Diaz ◽  
Jorge Duarte Forero ◽  
Jesus Garcia ◽  
Adriana Rincon ◽  
Armando Fontalvo ◽  
...  
Keyword(s):  
Heat Engine ◽  
Ideal Gas ◽  
Operating Conditions ◽  
Plant Performance ◽  
Working Fluid ◽  
Thermal Plant ◽  
Piston Cylinder ◽  
Proposed Model ◽  
Size Constraints ◽  
Flow Resistances

The application of equilibrium thermodynamics in the study of thermal plant performance under real operating conditions is a constant challenge. In this paper, an analysis of a reservoir pressure piston working between two linear flow resistances is performed by considering the friction of the piston cylinder system on the walls. The proposed model is developed to obtain the optimum power output and speed of the piston in terms of first law efficiency. If the friction on the piston–cylinder assembly is neglected, the expressions obtained are consistent with those presented in the literature under laminar regime. It was also demonstrated that for both laminar and turbulent regimes with overall size constraints, the power delivered can be maximized by balancing the upstream and downstream flow resistances of the piston. This paper also evaluated the influence of the overall size constraints and flow regime on the performance of the piston cylinder. This analysis is equivalent to evaluate the irreversibilities in an endo-irreversible Carnot heat engine with heat loss resistance between the engine and its heat reservoirs. The proposed model introduced some modifications to the results obtained from the recent literature and led to important conclusions. Finally, the proposed model was applied to calculate the lost available work in a turbine operating at steady flow conditions with an ideal gas as working fluid.

Micro Surface Shaping for the High-Pressure Operation of Piston Machines With Water as a Working Fluid

2015 ◽  
Author(s):  
Meike H. Ernst ◽  
Monika Ivantysynova
Keyword(s):  
High Pressure ◽  
High Pressures ◽  
Working Fluid ◽  
Hydraulic Systems ◽  
Machinery Construction ◽  
Pressure Buildup ◽  
Piston Cylinder ◽  
Low Viscosity ◽  
Load Carrying ◽  
Surface Shaping

Oil is the main working fluid used in the hydraulics industry today — but water is nonflammable, environmentally friendly and cheap: it is the better choice of working fluid for hydraulic systems. However, there is one caveat. Water’s extremely low viscosity undermines its ability to carry load. In forest machinery, construction machinery, and aircraft systems, today’s hydraulic circuits have high operating pressures, with typical values between 300 and 420 bar. These high pressures create the need for high load-carrying abilities in the fluid films of the tribological interfaces of pumps and motors. The most challenging of these interfaces is the piston-cylinder interface of swashplate type piston machines, because the fluid must balance the entire piston side load created in this design. The low viscosity of the water turns preventing metal-to-metal contact into quite a challenge. Fortunately, an understanding of how pressure builds and shifts about in these piston-cylinder lubrication interfaces, coupled with some clever micro surface shaping, can allow engineers to drastically increase the load-carrying ability of water. As part of this research, numerous different micro surface shaping design ideas have been simulated using a highly advanced non-isothermal multi-physics model developed at the Maha Fluid Power Research Center. The model calculates leakage, power losses, film thickness and pressure buildup in the piston-cylinder interface over the course of one shaft revolution. The results allow for the comparison of different surface shapes, such as axial sine waves along the piston, or a barrel-shaped piston profile. This paper elucidates the effect of those surface profiles on pressure buildup, leakage, and torque loss in the piston-cylinder interface of an axial piston pump running at high pressure with water as the lubricant.

The Impact of Micro-Surface Shaping on the Piston/Cylinder Interface of Swash Plate Type Machines

2015 ◽  
Author(s):  
Ashley M. Wondergem ◽  
Monika Ivantysynova
Keyword(s):  
Surface Profile ◽  
Sine Wave ◽  
Operating Conditions ◽  
Surface Shape ◽  
Hydrodynamic Bearing ◽  
Piston Cylinder ◽  
Wide Range ◽  
Surface Shaping ◽  
Pumping Mode ◽  
The Impact

With the wide use of axial piston machines of the swashplate type in industry, it is essential to maximize the overall efficiency of the machines. Focusing on the piston-cylinder interface, as it performs as a hydrodynamic bearing simultaneously fulfilling a sealing function, the overall machine can be improved by reducing the power losses due to viscous friction and leakage flow of this interface. This paper presents a research study in regards to altering the geometry of the piston through micro-surface shaping influencing the generation of the fluid film between the piston and the cylinder. This investigation utilizes a novel fully coupled fluid structure interaction model considering both thermal and elastic deformations of the solid bodies to predict the phenomena occurring within the fluid gap. Encompassed in this simulation study is a diversity of piston micro-surface shapes and a wide range of machine operating conditions. The designs presented include an axial sine wave, a flat, cylindrical design with tapered ends, a barreled shape, a combination of the axial sine wave and barrel, along with a circumferential sine wave. High pressure operating conditions in pumping mode as well as common operating conditions in both pumping and motoring mode are considered for the various designs. The results demonstrate up to a 30% reduction in energy dissipation from a standard piston-cylinder interface at higher pressure operating conditions (over 15% reduction considering all three interfaces of the machine) with the addition of a barrel surface shape while a 25% reduction (over 5% overall) is achievable at lower operating pressures in pumping mode with a waved barrel surface profile. As for motoring mode a 30% reduction (around 10% overall) is possible with the introduction of a waved barrel surface profile on the piston. It will also be shown, that not only are these reductions possible though microsurface shaping of the piston, but the reliability of the machine is also improved by reducing run-in wear all while maintaining a cost-effective, manufacturable design.

The Impact of the Surface Shape of the Piston on Power Losses

2014 ◽  
Author(s):  
Ashley M. Wondergem ◽  
Monika Ivantysynova
Keyword(s):  
Energy Dissipation ◽  
Cost Effective ◽  
Operating Conditions ◽  
Surface Shape ◽  
Critical Gap ◽  
Piston Cylinder ◽  
Wide Range ◽  
Load Carrying ◽  
Gap Height ◽  
The Impact

Axial piston machines are widely used in industry thus new cost-effective and highly efficient designs are needed. One way to increase efficiency and decrease cost is by altering the geometry along with the configuration of the piston/cylinder interface influencing the fluid film generation and in turn the energy dissipation and load carrying capacity while still having a design that is cost effective and easy to manufacture. This paper presents a study on a reduction of energy dissipation between the piston and cylinder over a wide range of operating conditions at both full and partial displacements based on the surface shape of the piston along with the minimum clearance. First, it is necessary to measure a base design and then compare those results to simulations in order to verify the simulation results. Once a baseline is established, various piston surface shapes and minimum clearances are then also simulated and compared back to the simulated baseline. Not only is energy dissipation important to compare, but also the minimum gap height over one revolution. The minimum gap height is in direct correlation to friction loss and wear. Therefore, this paper also includes an understanding of how the gap height affects the total losses thus leading to the importance of finding a relative clearance that satisfies a median between torque losses and leakage along with the importance of reducing the occurrence of critical gap heights to reduce the need for wear in in the machine.

scholarly journals Experimental Investigation of a Small-Scale ORC Power Plant Using a Positive Displacement Expander with and without a Regenerator

Energies ◽  
2019 ◽  
Vol 12 (8) ◽  
pp. 1452 ◽  
Author(s):  
Collings ◽  
Mckeown ◽  
Wang ◽  
Yu
Keyword(s):  
Heat Exchanger ◽  
Power Plants ◽  
Large Scale ◽  
Internal Heat ◽  
Expansion Ratio ◽  
Operating Conditions ◽  
Working Fluid ◽  
Small Scale ◽  
Regenerative Heat ◽  
Positive Displacement

While large-scale ORC power plants are a relatively mature technology, their application to small-scale power plants (i.e., below 10 kW) still encounters some technical challenges. Positive displacement expanders are mostly used for such small-scale applications. However, their built-in expansion ratios are often smaller than the expansion ratio required for the maximum utilisation of heat sources, leading to under expansion and consequently higher enthalpy at the outlet of the expander, and ultimately resulting in a lower thermal efficiency. In order to overcome this issue, one possible solution is to introduce an internal heat exchanger (i.e., the so-called regenerator) to recover the enthalpy exiting the expander and use it to pre-heat the liquid working fluid before it enters the evaporator. In this paper, a small-scale experimental rig (with 1-kW rated power) was designed and built that is capable of switching between regenerative and non-regenerative modes, using R245fa as the working fluid. It has been tested under various operating conditions, and the results reveal that the regenerative heat exchanger can recover a considerable amount of heat when under expansion occurs, increasing the cycle efficiency.

Effect analysis of silencing grooves on pressure and vibration characteristics of seawater axial piston pump

2016 ◽  
Vol 231 (8) ◽  
pp. 1390-1409 ◽  
Author(s):  
Fanglong Yin ◽  
Songlin Nie ◽  
Wei Hou ◽  
Shuhan Xiao
Keyword(s):  
Three Dimensional ◽  
Vibration Characteristics ◽  
Operating Conditions ◽  
Piston Pump ◽  
Axial Piston Pump ◽  
Effect Analysis ◽  
Compressibility Effect ◽  
Low Viscosity ◽  
Dynamics Simulations ◽  
Axial Piston

Seawater axial piston pump is a critical power component in seawater fluid power system. As the properties of high bulk modulus and low viscosity of seawater, the pressure and vibration characteristics of the seawater axial piston pump will be getting poorer than the traditional oil pump. In this study, the pressure, flow, and vibration characteristics for a seawater axial piston pump are investigated. The three-dimensional computational fluid dynamics simulations for the port plate with non-grooved, U-shaped, and triangle-based pyramid silencing groove designs have been conducted over a range of operating conditions, which consider the fluid compressibility effect and cavitation damage. Measurements of pressure ripple and pump vibration are carried out at various loading conditions to verify the results of simulation. The experiment turned out that the well-designed port plate can mitigate both pressure ripples as well as vibrations of the pump. This research will lay the foundation for the further development of a low fluid noise seawater axial piston pump.

Novel Pressure Adaptive Piston Cylinder Interface Design for Axial Piston Machines

2019 ◽  
Author(s):  
Shanmukh Sarode ◽  
Lizhi Shang
Keyword(s):  
Interface Design ◽  
Interaction Model ◽  
Cost Effective ◽  
Operating Conditions ◽  
Pressure Effects ◽  
Cylinder Block ◽  
Design Solution ◽  
Piston Cylinder ◽  
Standard Design ◽  
Axial Piston

Abstract The paper presents a novel concept of a pressure adaptive piston/cylinder interface design for a swashplate type axial piston machine that uses a pressurized groove around the bushing inside the cylinder block. This groove is connected to the pump displacement chamber and it uses pressure deformations of the bushing to improve the sealing function of the piston/cylinder lubricating interface. Such a design concept is based on a groove design that is easy to manufacture, thus resulting in a cost-effective design solution. The proposed piston/cylinder interface design is simulated using a multi-domain simulation model developed by the authors’ research team. The tool is particularly suitable for the analysis of the internal gap flows, being based on a fully coupled fluid structure thermal interaction model, which calculates the non-isothermal gap fluid behavior considering solid body deformations due to temperature and pressure effects. The proposed solution is compared in simulation with respect to a standard design of an axial piston pump. The results indicate that the proposed pressure adaptive piston/cylinder interface is able to improve the sealing function of the piston/cylinder interface at different operating conditions. Therefore, the proposed novel design can be seen as a possible method to increase the energy efficiency of the current designs of swash plate units.

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