Fluid borne noise in vane type hydraulic transmission systems

Abstract

A computer model was developed for a radial vane pump, possessing a new configuration with twin abutments and retractable vanes. The model computes the flow and pressure histories of the segment and port, based on compressibility, leakage and geometry effects. The equation describing the general flow processes is a non-linear first order differential equation, and under specific conditions can be simplified or approximated to a form amenable to a quick solution. The program incorporates a separate algorithm enabling the utilisation of this time saving feature. The combined effects of compressibility, and of segment and port compression mis-match results in high levels of fluid flow ripple. Resistive flow paths (relief grooves), enable correct segment compression by providing adequate leakage from the ports. The program was used to assess the levels of flow ripple and the effectiveness of relief grooves. Direct measurement of flow ripple is hindered by requirements of high dynamic response, and existing techniques are expensive and complicated. However, dynamic pressure measurements may be used to determine the flow ripple levels. The relationship between the dynamic levels of flow and pressure is dependant on standing wave and other system effects. A technique, utilising transmission line theory, has been developed which enables the deconvolution of individual flow ripples from standing wave and superposition effects. The pump model has been found to correlate well with actual measurements. Using the model, silencing grooves have been found to be effective in reducing the amplitude of the flow ripple over a wide range of operating conditions. In the pump tested, a 5.4 dB reduction was achieved. Greater reductions are expected under more typical conditions. In tests, the technique of wave deconvolution was effective in recovering the required data with a typical error of 5 percent.