Muffler for a cooling system of an electric motor

• US 5,183,975 A
• Filed: 05/15/1991
• Issued: 02/02/1993
• Est. Priority Date: 05/15/1991
• Status: Expired due to Term

• Current Assignee: Siemens Industry Incorporated (Siemens AG)
• Original Assignee: Siemens Energy & Automation Incorporated (Siemens AG)
• Inventors: Craggs, Jack L., Burke, Robert R.
• Primary Examiner(s): Gellner, Michael L.
• Assistant Examiner(s): Dang, Khanh
• Application Number:
  US07/700,300
• Time in Patent Office: 629 Days
• Field of Search: 181/202, 181/224, 181/200, 181/205, 181/207, 181/208, 181/209, 310/51
• US Class Current: 181/202
• CPC Class Codes: H02K 5/24 specially adapted for suppression or reduction of noise or vibrations
• CPC Class Codes: H02K 9/02 by ambient air flowing through the machine

Abstract

A muffler for an air-cooling system used for channeling air for cooling an electric motor comprises a housing mounted on the electric motor and formed with an air inlet; and an air outlet and an air passage extending between and connecting the inlet and the outlet. Air from outside the housing employed to cool the motor enters through the inlet, flows through the passage and exits through the outlet. Noise having a spectrum of frequencies including a relatively low main discrete frequency, which corresponds to a relatively long wave-length, and a plurality of higher frequencies is generated in the cooling air during operation of the motor and its cooling system. A baffle is positioned within the housing adjacent to the outlet to interrupt lines of sight from the air passage to the outside of the housing. The housing and the baffle are made of a metal or plastic and have sufficient mass to attenuate the higher frequencies of the noise spectrum to a substantial degree. A sound-absorbent material is positioned on the interior surfaces of the housing and has 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, outlet, and air passage are of large cross section to enable cooling of the motor using low air velocities at low back pressures. The inlet and outlet are located relative to the motor and direct exhaust air in such a manner as to minimize recirculation of the air.

Claims

1. 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.

2. A muffler according to claim 1 wherein the electric motor has rotor bars and the relatively low main discrete frequency is equal to the passing frequency of the rotor bars with respect to a reference point when the motor is in operation.

3. A muffler according to claim 2 wherein the passing frequency is within the range of 0.5 kHz to 4 kHz.

4. A muffler according to claim 1 wherein the predetermined material is a metal.

5. A muffler according to claim 1 wherein the predetermined material is a plastic.

6. A muffler according to claim 1 wherein the sound-absorbent material is selected from the group consisting of fiberglass and polyurethane foam.

7. A muffler according to claim 1 wherein the electric motor has axial and radial directions that are mutually orthogonal and wherein the cooling air enters the motor axially and exits the muffler radially.

8. A muffler according to claim 1 wherein the electric motor has axial and radial directions that are mutually orthogonal and wherein the cooling air enters the motor radially and exits the muffler axially.

9. In combination, an electric motor and a pair of mufflers mounted on opposite sides thereof, each muffler being constructed in accordance with claim 1.

10. A muffler for an air-cooling system used for channeling air for cooling a motor having a rotor, the muffler comprising:

a housing mounted on the motor and formed with an inlet, an outlet and a passage extending between and connecting the inlet and the outlet, whereby air from outside the housing employed to cool motor enters the housing through the inlet, flows through the passage and exits the housing through the outlet and generates noise having a spectrum of frequencies including a relatively low main discrete frequency and a plurality of higher frequencies;

a baffle positioned within the housing adjacent to the outlet means so as to interrupt lines of sight from the passage to the outside of the housing;

a sound-absorbent material positioned on selected interior surfaces of the housing means, and

said inlet, outlet and passage having a large cross section chosen so that air velocity in the housing is less than 20% of peripheral speed of the rotor when the motor is in operation.

11. The muffler of claim 10 when the relatively low main discrete frequency is equal to the passing frequency of the rotor bars with respect to a reference point when the motor is in operation.

12. The muffler of claim 11 wherein the passing frequency is within the range of 0.5 khz to 4 khz.

13. The muffler of claim 10 wherein the housing is made of metal.

14. The muffler of claim 10 wherein the housing is made of plastic.

15. The muffler of claim 10 wherein the baffle is made of plastic.

16. The muffler of claim 10 wherein the sound-absorbent material is selected from a group consisting of fiberglass and polyurethane foam.