Prediction of Pump Dynamics Utilizing Computer Simulation Model- With Special Reference to Noise Reduction 2000-01-2632

This paper is the result of a masters thesis project that has been performed for Parker Hannifin at Abex NWL Aerospace Hydraulics in Kalamazoo, MI and at Central Engineering in Irvine, CA from September 1999 through February 2000 by Andreas Johansson [1].

One of the major drawbacks with hydraulic powered systems is the disturbing noise level. A main source of noise is the hydraulic pump. The noise is mainly created by the large alternating forces inside the pump, but also by the pump generated flow ripple. There are two different kinds of flow ripple. The first kind is the kinematic flow ripple, which is caused by the limited numbers of pistons. The other kind is the dynamic flow ripple, due to the compressibility of the fluid. The compressibility effects are obvious when the fluid is subjected to large alternating pressures, which is the case for hydraulic pumps. In a system, the flow ripple transforms to pressure ripple, which creates noise. Besides the noise aspect, the resulting pressure ripple and associated vibration shorten the fatigue life of system components and can even cause breakdown and control instability.

This paper concerns the dynamic behavior of a hydraulic axial piston pump. A part of this paper describes the development of a computer simulation model. With the model, it is possible to make a detailed dynamic analysis of pump flow ripple and investigate different ways to reduce its magnitude. In the model, it is very easy to create the desired pump geometry in a data file for simulation. The model also facilitates parametrical studies and optimization of pump geometry, resulting in reduction of discharge flow ripple while controlling the amplitude and mean value of swash-plate reaction torque variations. The starting point for the pump model was an already existing model for flow ripple analysis in axial piston machines, developed by Dr Weddfelt and Dr Pettersson from the Division of Fluid and Mechanical Engineering Systems at Linköping University in Sweden. The model has been extensively verified by experiments.

The mathematical representation of the simulation model includes design features such as pre-compression, post-expansion, pressure relieve grooves, pre-compression filter volumes and post-expansion filter volumes. The pump model provides a wealth of useful information to the product designer.

Irvine, California, February 2, 2000