Dynamic characterization of engine mount at different orientation using sine swept frequency test

Rubber engine mounts are commonly used to provide vibration attenuation. The loss factor and dynamic stiffness of engine mount provide fundamental information of the energy dissipation. The objectives of this work are to study the frequency-dependant stiffness and loss factor of engine rubber mount and to determine the effect of the orientation angle of the engine mount on the dynamic characteristics. The test consists of three engine mounts, shaker, an accelerometer , analyzer and force transducer with a preload mass of 2.72 kg steel plate mounted on the engine mounts. The plate is excited at the center and the input force and response is measured at the point of excitation which is called the driving point excitation. The electromagnetic shaker is used as an excitation source to excite the rubber engine mount system to obtain the frequency response function and dynamic stiffness of rubber mounts. The resulting signals captured from the force transducer and accelerometer are then analyzed using LMS spectral testing. The frequency response function (acceleration/ force) is estimated using the two channels FFT calculation where the dynamic stiffness is the reciprocal of frequency response function. The real and imaginary parts of dynamic stiffness can be obtained directly from the sine swept frequency test. The frequency response function and dynamic stiffness of engine are measured from sine swept frequency test for frequency range of )-200 Hz. The unity value in coherence function within the range above 10 Hz shows the linear dependency between force and displacement signals. The figure shows that the dynamic stiffness is frequency dependent. The dynamic stiffness is increasing when the frequency increased after the resonance at 40 Hz. For the excitation frequency before resonance, the dynamic stiffness decreased while the excitation frequency increased. Minimum dynamic stiffness is found at resonant frequency and the values of dynamic stiffness increased when the frequency increases above the natural frequency. The frequency which natural frequency of the system occurred becomes lower when the engine mount orientation is changed from 0 degree (axial) to 90 degrees (normal). At the same time, the values of dynamic stiffness decreases especially at the frequencies below the natural frequency. The measured stiffness and loss factor are validated by comparing the reconstructed system frequency response function of the single DOF system using the estimated frequency dependent stiffness and loss factor to that frequency response function which is obtained from direct sine swept test. Comparison between measured and estimated FRF showed that the correlation between the two FRFs is good at high frequencies especially away from the resonance.