Single cavity automobile muffler

• US 5,272,286 A
• Filed: 05/04/1992
• Issued: 12/21/1993
• Est. Priority Date: 04/09/1990
• Status: Expired due to Term

• Current Assignee: Noise Cancellation Technologies, Inc. (NCT Group, Inc.)
• Original Assignee: Active Noise and Vibration Technologies, Inc.
• Inventors: Barnes, Dennis, Cain, John J., Dye, David A.
• Primary Examiner(s): Gellner, Michael L.
• Assistant Examiner(s): Dang, Khanh
• Application Number:
  US07/879,517
• Time in Patent Office: 596 Days
• Field of Search: 181/206, 381/71, 60/312
• US Class Current: 181/206
• CPC Class Codes: F01N 1/065 by using an active noise source, e.g. speakers
• CPC Class Codes: F01N 1/20 having oscillating or vibrating movement the parts being resilient walls F01N1/22
• CPC Class Codes: F01N 1/22 the parts being resilient walls
• CPC Class Codes: G10K 2210/32272 Helmholtz resonators

Abstract

A noise suppression system for use on internal combustion engines and small enough for use in automotive applications is disclosed. A cancellation noise generator and actuator speakers produce a noise to combine with and cancel the engine noise carried in exhaust gases in a mixing chamber. The resultant noise leaving the mixing chamber is measured by a circular tubular microphone array to control the noise generator.

Claims

1. A system for reducing undesirable noise emanating from an output end of a duct through which output end a gaseous fluid discharges in a stream to a surrounding atmosphere, said system comprising:

a) audio input means for sensing noise emanating from said duct at a location external to said duct which audio input means generates an noise-related control signal;

b) a cancellation nose generator responsive to said control signal having an output external to said duct and generating a cancellation noise wave;

c) a walled mixing chamber at said output end of the duct and external to the duct into which mixing chamber the duct discharges;

d) an output port to atmosphere from said mixing chamber; and

e) a cancellation chamber receiving said cancellation noise wave from the cancellation noise generator and opening into said mixing chamber to be acoustically coupled therewith;

wherein said walled mixing chamber is configured for combining the undesirable noise and the cancellation noise wave without substantially constraining said stream of gaseous fluid whereby undesirable noise emanating from the output end of the duct passes through said mixing chamber for cancellation before discharging to the atmosphere.

2. A system according to claim 1, wherein said cancellation chamber extends annularly around said outlet end whereby undesired noise radiating from said outlet end or from gaseous fluid discharging therefrom is subject to mixing with and reduction by said cancellation noise wave.

3. A system according to claim 1 wherein said audio input means comprises an annular array of microphones distributed within an audio input chamber disposed around said gaseous discharge stream and disposed downstream of said mixing chamber.

4. A system according to claim 3, wherein said walled mixing chamber comprises a mixing pipe extending around and peripherally enclosing said mixing chamber and capable of extending around the output end of said duct, said mixing pipe having an upstream end communicating with said duct at the open end thereof and having a downstream end open to atmosphere.

5. A system as in claim 4 wherein said mixing pipe is substantially concentric with said gaseous fluid discharge stream said annular array of microphones is arranged substantially concentrically with both the direction of said gaseous fluid discharge stream and the mixing pipe.

6. A system as in claim 3 which includes said duct, wherein said walled mixing chamber includes a chamber member which together with said cancellation noise generator and said duct defines a single cancellation signal chamber.

7. A system as in claim 3 wherein the duct output end is contained within the mixing chamber, said mixing chamber is downstream of said output end and said cancellation chamber opens into said mixing chamber at points upstream of the duct output end.

8. A system as in claim 7, wherein said cancellation noise generator is a first audio loudspeaker having a front surface which is acoustically coupled to said mixing chamber and a rear surface.

9. A system as in claim 8, wherein a cancellation signal volume comprises a front cancellation volume defined between said duct and said mixing chamber member and forming a front volume of a ported audio enclosure system, said cancellation signal volume further comprising a closed rear volume acoustically coupled to the rear surface of said first loudspeaker.

10. A system as in claim 9, wherein said audio input means comprises a closed tubular loop having an interior and having at least one microphone acoustically coupled to said interior and comprises a plurality of holes disposed in said tubular loop, said tubular loop being disposed substantially around said output port.

11. A system as in claim 9, further comprising a second loudspeaker positioned, configured and dimensioned to generate a signal substantially symmetrical with respect to the cancellation noise generated by said first loudspeaker.

12. A system as in claim 1, wherein a cancellation signal volume comprises a front cancellation volume defined between said duct and said mixing chamber member and forming a front volume of a ported audio enclosure system, said cancellation signal volume further comprising a closed rear volume defining member acoustically coupled to the rear surface of said cancellation noise generator.

13. A system as in claim 12, wherein said audio input means comprises a tubular loop having an interior and having at least one microphone acoustically coupled to said interior and comprises a plurality of holes disposed in said tubular loop, said tubular loop being disposed substantially around said output port.

14. A system as in claim 13, further comprising a second cancellation noise generator positioned, configured and dimensioned to generate a signal at a point substantially symmetrical with respect to the cancellation noise generated by said cancellation noise generator.

15. A system as in claim 12, further comprising a second loudspeaker positioned, configured and dimensioned to generate a signal substantially symmetrical with respect to the cancellation noise generated by said first loudspeaker.

16. A system for preventing undesirable noise from emanating from an output end of an inner ducting arrangement, said system comprising said inner ducting arrangement, a plurality of audio inputs disposed around said output end of said inner ducting arrangement for sensing noise at said output end and generating a control signal, a cancellation noise generator responsive to said control signal and including a cancellation chamber having an output acoustically coupled to a walled mixing volume defined within an outer ducting arrangement, said generator generating a cancellation noise, and said audio inputs being positioned outside said mixing volume, said mixing volume being configured for combining the undesirable noise and the cancellation noise to cancel a substantial portion of the undesirable noise.

17. A system as in claim 16, wherein said plurality of audio inputs comprises a tubular member having an interior, at least one microphone acoustically coupled to said interior and a plurality of holes disposed in said tubular member, said tubular member being disposed substantially around said output end.

18. A system as in claim 17, wherein said tubular member is closed and said cancellation noise generator is a loudspeaker, having front and rear surfaces and a volume defined by said outer ducting arrangement forms a front volume of a ported audio enclosure system and further comprising a closed rear volume defining member acoustically coupled to the rear surface of said loudspeaker.

19. A system as in claim 17, further comprising a second loudspeaker positioned, configured and dimensioned to reinforce the cancellation noise generated by said first loudspeaker.

20. A system for preventing undesirable noise from emanating from an output end of a device, said system comprising the device, a plurality of audio inputs for sensing noise at said output end and generating a control signal, a cancellation noise generator for generating a cancellation noise in response to said control signal and having an output acoustically coupled to a mixing volume acoustically coupled to receive said undesirable noise, said mixing volume being configured for combining the undesirable noise and the cancellation noise to cancel a substantial portion of the undesirable noise, said plurality of audio inputs comprising a tubular member having an interior and having at least one microphone acoustically coupled to said interior and a plurality of holes disposed in said tubular member.

21. A system as in claim 20, wherein said tubular member is disposed substantially around said output end.

22. An automotive noise suppressor for reducing noise emitted from an internal combustion engine, comprising:

(a) an exhaust duct coupled to said internal combustion engine, defining an inside passage for exhausting hot gases and having an output end;

(b) an outer casing having an output port, said outer casing surrounding said exhaust duct and extending in length beyond said output end of said exhaust duct to define a protected space between said exhaust duct and a portion of the inside surface of said outer casing and a mixing space acoustically coupled to said protected space and adjacent said output end of said exhaust duct;

(c) heat insulative material secured to the portion of said exhaust duct adjacent said protected space;

(d) an audio transducer positioned adjacent and acoustically coupled to said protected space and remote from said mixing space;

(e) a cancellation signal generator having an output coupled to said audio transducer; and

(f) a microphone positioned at a point downstream of said mixing space for generating an audio feedback signal, said audio feedback signal being coupled to said cancellation signal generator to cause said cancellation signal generator to drive said audio transducer to generate an audio signal which will cancel a substantial portion of said noise emitted from said internal combustion engine.

23. A noise suppressor as in claim 22, wherein said audio transducer has a front surface and a rear surface, said protected space forming a front volume of a ported audio enclosure system, said front surface being acoustically coupled to said front volume and further comprising a closed rear volume acoustically coupled to the rear surface of said audio transducer.

24. A noise suppressor as in claim 23, comprising a tubular loop having an interior, at least one microphone acoustically coupled to said interior and having a plurality of holes disposed in said tubular loop.

25. A noise suppressor as in claim 22, comprising a tubular loop having an interior, at least one microphone acoustically coupled to said interior and having a plurality of holes disposed in said tubular loop.

26. A noise suppressor as in claim 25, wherein said holes are disposed around said output port of said outer casing.

27. A noise suppressor as in claim 25, wherein said tubular loop is disposed substantially around said output port.

28. A noise suppressor as in claim 25, further comprising a second audio transducer positioned, configured and dimensioned to generate a signal substantially symmetrical with respect to an audio signal generated by the first said audio transducer.

29. A noise suppressor as in claim 27, wherein audio transducer is a loudspeaker comprising a cone, a resilient member for supporting said cone and an electromechanical transducer-driver.

30. An automobile noise suppressor for reducing noise emitted from an internal combustion engine, comprising:

(a) an exhaust duct coupled to said internal combustion engine, said exhaust duct defining an inside passage for exhausting hot gases and having an output end;

(b) an outer casing having an output port, said outer casing symmetrically surrounding said exhaust duct and extending beyond said output end of said exhaust duct to define a protected space between said exhaust duct and a portion of an inside surface of said outer casing and a mixing space acoustically coupled to said protected space and adjacent said output end of said exhaust duct;

(c) wall structure disposed between said protected space and said exhaust duct, said wall structure being in facing spaced relationship to said exhaust duct and positioned, configured and dimensioned to define an acoustic passage between said protected space and said mixing space;

(d) a plurality of audio transducers positioned adjacent and acoustically coupled to said protected space;

(e) a cancellation signal generator having an output coupled to said audio transducers; and

(f) a microphone positioned at a point downstream of said mixing space for generating an audio feedback signal, said audio feedback signal being coupled to said cancellation signal generator to cause said cancellation signal generator to drive each said audio transducers to generate an audio signal which will cancel a substantial portion of said noise emitted from said internal combustion engine.

31. A noise suppressor as in claim 30, wherein said audio transducer comprises a pair of loudspeakers each having a front surface and a rear surface, said protected volume forming front volumes of a pair of respective ported audio enclosures, said front surfaces being acoustically coupled to respective ones of said front volumes and further comprising a pair of closed rear volumes acoustically coupled to a respective one of said rear surfaces of said loudspeakers.

32. A noise suppressor as in claim 31, comprising a tubular loop having an interior, at least one microphone acoustically coupled to said interior and having a plurality of holes disposed in said tubular loop.

33. A system for reducing undesirable noise emanating from an output end of a duct though which output end a gaseous fluid discharges in a stream to a surrounding atmosphere generally in a direction away from said duct, said system comprising:

a) audio input means for sensing noise emanating from said duct at a location external to said duct which audio input means generates a noise-related control signal;

b) a cancellation noise generator responsive to said control signal and which generates a cancellation noise wave; and

c) means acoustically to couple said cancellation noise wave with said undesirable noise thereby to reduce said noise;

wherein said audio input means comprises;

d) an arcuate audio input chamber; and

e) a plurality of audio input devices distributed within said audio input chamber;

and wherein said audio input chamber is disposed around said stream of gaseous fluid to receive sound therefrom, has a protective wall between the gaseous flow and the audio input devices, and has means to admit sound from the gaseous fluid flow to the audio input chamber whereby said audio input chamber can serve to smooth said noise emanating from said duct for input to the input device.

34. A system according to claim 33 wherein said audio input chamber is annular and said audio input devices are disposed symmetrically therearound.

35. A noise suppressor for reducing noise emitted from an output of a device, comprising:

a duct configured and dimensioned to be coupled at an input end to the output of said device, said duct defining an inside passage and having an output end;

an outer casing having an output port surrounding said duct and extending in length beyond said output end of said duct to define a first space between said duct and a portion of the inside surface of said outer casing and a mixing space acoustically coupled to said first space and adjacent said output end of said duct;

a plurality of audio transducers positioned adjacent and acoustically coupled to said first space and remote from said mixing space each of said plurality of audio transducers being oriented to generate an audio signal in a direction angular to that of said other audio transducers;

a cancellation signal generator having an output coupled to said audio transducers; and

a microphone positioned at a point downstream of said mixing spaced for generating an audio feedback signal, said audio feedback signal being coupled to said cancellation signal generator to cause said cancellation signal generator to drive said audio transducers to generate said audio signals which will cancel a substantial portion of said noise emitted from said device, said first mixing spaces being substantially open to an environment around said device.

36. An automobile noise suppressor for reducing noise emitted from an output end of an exhaust duct that is connected to an internal combustion engine to communicate exhaust gases therefrom, the noise suppressor comprising:

an outer casing having an output port, said outer casing surrounding said exhaust duct with said output port adjacent said output end of said exhaust duct, and including a wall structure defining a first and second compartment between said exhaust duct and a portion of an inside surface of said outer casing and an acoustic passage communicating each said compartment to said output port of said of said outer casing;

a first audio transducer positioned adjacent and acoustically coupled to at least a first one of said first compartment;

a second audio transducer positioned adjacent and acoustically coupled to at least a second one of said second compartment;

a cancellation signal generator having at least first and second outputs respectively coupled to said first and second audio transducers; and

a microphone positioned at a point downstream of said output port for generating an audio feedback signal, said audio feedback signal being coupled to said cancellation signal generator to cause said cancellation signal generator to drive said first of audio transducer to generate a first audio signal and to drive said second audio transducer to generate a second audio signal, different from said first audio signal.

37. The noise suppressor of claim 36, wherein the acoustic passage includes means separately communicating said first and second audio signals to the output port to cause cancellation of a portion of said noise emitted from said internal combustion engine.

38. The noise suppressor of claim 36, wherein the first audio signal contains audio frequencies predominantly in a frequency range higher than the audio frequencies predominantly contained in the second audio signal.

39. The noise suppressor of claim 38, wherein the first audio transducer has a frequency response substantially in the range of 200 Hz-600 Hz.

40. The noise suppressor of claim 38, wherein the second audio transducer has a frequency response substantially in the range of 20 Hz-200 Hz.

41. The noise suppressor of claim 36, said wall structure including means separating the first chamber from the second chamber.

42. The noise suppressor of claim 41, wherein said acoustic passage includes means for communicating the first chamber, to the output port of the outer casing separately from the second chamber.

43. The noise suppressor of claim 36, the outer casing including a mixing volume being configured for receiving and combining the exhaust gases from the duct and said first and second audio signals to cancel a substantial portion of the noise.

44. The noise suppressor of claim 36, including a tubular member having an interior, said microphone being acoustically coupled to said interior and a plurality of holes disposed in said tubular member, said tubular member being positioned downstream of said output port of said outer casing.