Muffler for a cooling system of an electric motor

A muffler for an air-cooling system used for channeling air for cooling heat-generating apparatus, the muffler comprising:

• housing means mounted on the heat-generating apparatus and formed with air-inlet means, air-outlet means and air-passage means extending between and connecting the inlet means and the outlet means, whereby air from outside the housing means employed to cool the heat-generating apparatus enters the housing means through the inlet means, flows through the passage means and exits the housing means through the outlet means, noise having a spectrum of frequencies including a relatively low main discrete frequency, which corresponds to a relatively low wavelength, and a plurality of higher frequencies being generated in the cooling air during operation of the heat-generating apparatus and cooling system;
• baffle means positioned within the housing means adjacent to the outlet means to interrupt lines of sight from the passage means to the outside of the housing means;
• the housing means and the baffle means being made of a predetermined material having a predetermined mass, the material and mass being selected to attenuate direct egress of the higher frequencies of the noise spectrum to a substantial degree;
• and
• a sound-absorbent material positioned on selected interior surfaces of the housing means and having an effective thickness equal to between approximately one-eighth and one-half of the wavelength of the relatively low main discrete frequency of the noise spectrum;
• the inlet means, outlet means and air-passage means being of large cross section to enable cooling of the heat-generating apparatus using low air velocities at low back pressures;
• and
• the inlet means and the outlet means being located relative to the heat-generating apparatus and directing exhaust air in such a manner to minimize recirculation of the air,
• wherein the heat generating apparatus is an electric motor having a rotor and the cross section of the inlet means, outlet means and air-passage means being chosen so that the air velocity in the housing is less than 20% of peripheral speed of the rotor when the motor is in operation.