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A new method, the “3 Pressures/ 2 Systems” method, is developed for determining source flow ripple and internal impedance of fluid power pumps. The method integrates exclusively an on-line measurement technique for the speed of sound in the fluid and a technique for eliminating flow disturbance effect on pressure sensors into the basic principle used in the existing “2 Pressures / 2 Systems” method. The new method has an inherent potential to yield results with higher accuracy and higher confidence. The high accuracy of the method is confirmed by the comparison of measured and predicted pressure ripple in a pump-pipe-valve system. Then, the method is applied to automotive fluid power pumps - power steering pumps. The measured results of source flow ripple and internal impedance are presented.

The paper presents the results of a study on the experimental determination and theoretical prediction of the source flow ripple generated by a fluid power piston pump. This work supports the development of quieter pumps with better fluidborne noise characteristics. As an effective experimental method, the “2 Pressures/2 Systems” method is introduced and used to determine the actual value of the source flow ripple and confirm the prediction results. A theoretical model is derived by the inclusion of the compressibility of the fluid, the fluid momentum in the cylinder chamber and relief grooves, and the pressure-dependent effective bulk modulus of the fluid containing air. The accuracy of the model is confirmed by the comparison of predicted and measured results. Finally, the effectiveness of the experimental method is presented.

A tuning cable and hose device, i.e. a flexible metal tuning cable placed coaxially inside a section of hose, is usually used in power steering hydraulic circuits to reduce pressure pulsations in the circuits. To evaluate the fluidborne noise attenuation characteristics of tuning cable and hose devices correctly, a new evaluation method, based on the experimental determination of transmission loss of the tuning cables and hoses, is proposed here. The effectiveness of the method and test system are confirmed. The results obtained are valuable for design optimization and theoretical modeling of hydraulic power steering systems and other similar hydraulic systems.