On the pressure ripple measurement in variable displacement vane pumps

Vane pumps exhibit pressure ripple in the pressure evolution trend during a complete shaft rotation. Pressure ripple can determine oscillating forces within the system leading to vibration and noise generation. In this context, this paper is focused on the experimental measurement of the pressure evolution in vane pumps by using two different methodologies. Results of measurements are shown, highlighting advantages and disadvantages of both methodologies. In the first method a pressure transducer is directly facing the volume between two vanes, in the second method the sensor is located inside an external chamber where the oil is transferred via a ducts suitably designed in the rotor shaft. Briefly, the first method gives better results in terms of pressure evolution but involves some practical problems in the set up: the measurements exhibit pressure offsets strongly dependent on the tightening torque used for sensor mounting and negative pressure values in the low pressure region. The second method is simpler to set up but the results are influenced by the dynamical behavior of the measurement duct carrying oil. In order to avoid resonances of this duct, a vibro-acoustical finite element (FE) model of the oil cavity has been developed. The numerical frequency response functions obtained by the FE model have been used in order to optimize the geometry of the measurement duct, reducing the effects of the resonances of the oil ducts. It is shown that, using this improved methodology, the dynamical components of the measured pressure are not significantly influenced by the frequency response of the measurement duct when the outlet pressures is higher than 50 bar, while for lower outlet pressure the first resonance of the measurement duct is close to the main vane harmonics