A Novel Positive Displacement Axial Piston Machine With Bent Cylinder Sleeves

In this paper, an investigation of a novel positive displacement axial piston machine using a bent cylinder sleeve configuration is presented. The proposed design eliminates the side moments on the piston/cylinder interface, therefore, reduces the frictional loss and improves the total energy efficiency. A multi-physics elastohydrodynamic lubrication model was used to aid the design of the piston/cylinder and the cylinder block/port block interface. Then, a lumped parameter model was used to optimize the port block geometry. Groove geometry was chosen primarily to reduce flow ripple, tilting moment, and cavitation risk. To improve the housing stiffness, the lumped parameter model was combined with a finite element analysis. This ensured safety for the testing. In the end, steady-state experiments were performed on the prototype based on the ISO4409 normative. The unit’s speed was set to 500 rpm, then increased by 500 rpm until it reached 3000 rpm. The supply pressure was set to 20 bar. The outlet pressure was set to 70 bar at first, then increased by 50 bar until it reached 220 bar. The results show a remarkable volumetric efficiency with a peak of 99.5%. It is however noted that due to some of the issues with the initial iteration of the current design, there is a reduction in mechanical efficiency. The causes and possible future solutions to these issues are discussed in the manuscript.

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

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.

Advanced Virtual Prototyping of Axial Piston Machines

This paper explains how a combination of advanced multidomain numerical models can be employed to design an axial piston machine of swash plate type within a virtual prototyping environment. Examples for the design and optimization of the cylinder block/valve plate interface are presented.

Increasing the Power Density for Axial-Piston Swash-Plate Type Hydrostatic Machines

Power density is an assumed attribute of an axial-piston swash-plate type hydrostatic machine. As such, very little research has been conducted to examine the nature and limit of this machine's power density and the literature is all but void of this important topic. This paper is being written to fill this void, and to provide a thorough analysis of the machine's power density. This paper is also aimed at identifying the most significant parameters that may be adjusted to increase the power density for a typical machine. As shown in this research, the power density of an axial-piston machine depends upon four dimensionless quantities that are characteristic of the machine's rotating group. As it turns out, the allowable stress for the cylinder block is the most sensitive parameter that may be adjusted for increasing the power density of this machine. It is further shown that increasing the machine's swash-plate angle, and reducing the minimum overhang length for the pistons, will have a significant impact on the power density as well. It is significant to note that altering the number of pistons in the design has essentially no impact on the power density of the machine and therefore the selection of this design parameter must be based upon other design objectives. In conclusion, it is shown in this paper that the power density of a typical machine may be increased by as much as 64% by altering a few of these parameters within a realistic realm of constraint.

Experimental Analysis on Oil Film Properties of Plane Port Pair in Axial Piston Machine

To find some rules keeping good lubrication condition for plane port pair in high-performance axial piston pump or motor, especially in the very severe applications, a new test rig was built up to simulate the operational principle of port pair, and to form the lubricating oil film for representative parameter acquisition. This rig is principally characterized by supply pressure up to 30 MPa, accurate control of oil film thickness by separate oil circuit design and electrohydraulic feedback control. The tested oil film working properties was analyzed by comparison with theoretical or simulation references. Experiments show that film balance time and thickness are two key parameters for describing oil film properties, and that working condition factors such as supply pressure, lubricating fluid temperature also notably affects the film thickness and its configuration, but they don’t show equivalent action. Lubrication effects can be valued by the tested frictional torque change of port pair.