2001

Verho, Martti; Klinge, Paul

The role of the cooling ribs seems to be important for the noise created at the cover of an electric motor. Relatively high peak velocities at the top of the ribs, induced by simple mechanical amplification, can make the ribs quite effective sound radiators. Based on a simplified 2D-model, a cover with ribs radiates as effectively as a flexible plate without ribs, if the peak velocity at the top of the ribs is three times the velocity of the plate. If the ribs are considered non-flexible, the velocity magnification depends on the height of the ribs. In the studied case, the magnification factor was 3.7. If the dynamic effects of flexible ribs are taken into account, the magnification factor could be even higher. Measurements made on a running motor seem to indicate that this level of magnification is quite realistic.