Contribution to digital prototyping of axial piston pumps/motors

Dongjune Albert Kim, Purdue University

Abstract

There are two main design issues in digital prototyping of swash plate type axial piston machines. First, the design of the rotating group with its lubricating interfaces is critical to the operation of the swash plate type axial machine. Swash plate type axial piston machines have three main lubricating interfaces - the Piston/Cylinder, the Cylinder block/Valve plate, and the Slipper/Swash plate interface. These lubricating interfaces fulfill simultaneously a bearing and sealing function. The three interfaces represent the most critical design issue within the design process of the swash plate type axial piston machine because these interfaces determine the performance and reliability of the machine and are the main source of energy dissipation. Ivantysynova and her research group (2001, 2002, 2005, 2010, and 2012) have developed fully coupled fluid structure interaction models based on non-isothermal flow through the lubricating gap for the three lubricating interfaces of swash plate type axial piston machines. The models consider the macro and micro motion of movable parts such as the piston, slipper, and cylinder block as well as the deformation of solid bodies due to pressure and temperature for all three interfaces. These models were developed separately for each interface. However, viscous friction forces generated in one interface are transferred to other interfaces, i.e. the friction force generated between piston and cylinder will load the cylinder block and therefore must be considered when calculating the cylinder block valve plate interface. Also, the friction force generated in the gap between the slipper and swash plate will act on the piston/slipper assembly and therefore must be considered when balancing forces acting on the piston. The second design issue involves the valve plate design in the swash plate type axial piston machine. The valve plate is a non-rotating component in the axial piston machine that is located adjacent to the cylinder block. The valve plate connects the pump ports to the individual cylinder chambers. Proper valve plate design is essential for the high performance axial piston machine because the valve plate regulates the displacement chamber pressure profile in the axial piston machine. The pressure profile in the displacement chamber is important in regards to the axial piston machine operation because the pressure profile has a very significant influence on the resulting fluid film of each of the three interfaces, on moments acting on the swash plate, and flow ripple in the low/high pressure ports. The pressure in the displacement chamber transforms to the primary force acting on the piston/cylinder, cylinder block/valve plate, and slipper/swash plate interface. Because of the time dependent change of pressure in each cylinder chamber the resulting forces and moments are pulsating. In addition, the force acting on the slipper/swash plate transforms to the moments acting on the swash plate, which influence the controllability of the swash plate angle. The pulsating forces and moments acting on the swash plate not only have an influence on the controllability of the swash plate angle, but also represent one of the main sources of noise generated in the axial piston machine. The moment acting on the swash plate oscillates the swash plate and the end case simultaneously, which in the end results in audible noise. This noise source is often referred to as structure-borne noise (SBN). The other noise source, fluid-borne noise (FBN), is also related to the valve plate because FBN results mainly from flow ripple in the low/high pressure port. Flow ripple in the low/high pressure port is affected by the number of pistons of the axial piston machine, but it also has a strong relationship with the displacement chamber pressure. Therefore, the valve plate design significantly influences both SBN and FBN. And for this reason, much valve plate design research has been conducted in order to reduce noise in the axial piston machine. There are two types of valve plate noise reduction techniques: passive and active noise reduction technique. Of these two noise reduction techniques, the passive noise reduction technique has the advantage that it does not require any additional power source or system. However, this technique has the disadvantage that it is not effective for a wide range of operating conditions. Relief groove, pre-compression filter volume (PCFV), and cross port are examples of passive noise reduction techniques. In order to study these phenomena more accurately, Seeniraj and Ivantysynova developed a simulation tool, VpOptim, for valve plate simulation and optimization. VpOptim can be used for valve plate optimization by implementing relief grooves and the PCFV in the valve plate. (Abstract shortened by UMI.)

Degree

M.S.M.E.

Advisors

Ivantysynova, Purdue University.

Subject Area

Mechanical engineering

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