Abstract:
In an active noise cancellation system having exhaust noise and anti-noise initiating at sources positioned perpendicular to each other, a noise management arrangement having a noise cancellation enclosure containing a noise cancellation space. The space is in communication with a noise cancellation port and has an exit port coaxial with the noise cancellation port. An opening receives the exhaust noise from an exterior of the enclosure and communicates the exhaust noise into the space and directs the noise towards the exit port, thereby minimizing the exhaust noise that impinges upon the enclosure.

Description:
FIELD OF INVENTION  
       [0001]     The present invention relates generally to active noise cancellation systems for vehicles, and more particularly to the arrangements for coupling a noise cancellation system to an exhaust component of a vehicle.  
       BACKGROUND  
       [0002]     Active noise cancellation systems typically operate by creating a noise cancellation signal which is equal-in sound pressure and opposite in phase with a primary noise signal. When combined, the two signals would ideally cancel one another out thus reducing the total airborne noise produced by a machine or by a vehicle.  
         [0003]     Such systems may be employed to reduce noise produced by an engine exhaust in a motor vehicle. However, the actual implementation of coupling the acoustic output of an exhaust system and a noise cancellation signal may be problematic depending on the design constraints of the vehicle. For example, one known system employs a cylindrical prism routing a noise cancellation signal through an open end of a first cylinder, and exhaust gasses through a second cylinder perpendicularly connected to the a side wall of the first cylinder. The silenced exhaust gasses exit from the opposite end of the first cylinder. Such an arrangement requires joining the intersection of two cylinders and has proven difficult to execute reliably. Furthermore, the routing of the exhaust gasses impinges the gasses against the inside of the cylindrical prism creating turbulence within the cylindrical prism. This turbulence causes vibration of components and results in an undesirable secondary structure borne noise issue.  
       SUMMARY OF INVENTION  
       [0004]     Accordingly, one aspect of the present invention is to provide a noise management device which is desirable for use in a system having a noise cancellation signal and an exhaust stream arriving perpendicular to each other.  
         [0005]     Another aspect of the present invention is to provide a noise cancellation enclosure which reduces or eliminates turbulence within the enclosure.  
         [0006]     Yet another aspect of the present invention is to provide a noise cancellation system suitable for use in a vehicle having a side-exiting exhaust.  
         [0007]     In accordance with these aspects, a noise management arrangement is provided. In an active noise cancellation system having exhaust noise and anti-noise initiating at sources positioned perpendicular to each other, the noise management arrangement has a noise cancellation enclosure containing a noise cancellation space. The space is in communication with a noise cancellation port and has an exit port coaxial with the noise cancellation port. An opening receives the exhaust noise from an exterior of the enclosure and communicates the exhaust noise into the space and directs the noise towards the exit port, thereby minimizing the exhaust noise that impinges upon the enclosure.  
         [0008]     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood however that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.  
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0009]      FIG. 1  illustrates a plan view of an embodiment of a noise management device.  
         [0010]      FIG. 2  illustrates a side view of an embodiment of a noise management device.  
         [0011]      FIG. 3  illustrates a perspective view of a noise cancellation enclosure. 
     
    
     DETAILED DESCRIPTION  
       [0012]     The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application or uses.  
         [0013]      FIG. 1  illustrates a plan view of an embodiment of a noise management arrangement  1  having a noise cancellation enclosure  10  for combining the acoustic output of a vehicle exhaust component  40  with the acoustic output of an active muffler speaker enclosure  50 . The enclosure  10  may be formed from metal, such as aluminum. The noise cancellation enclosure  10  has an arcuate wall  16 . The arcuate wall  16  is substantially planar in the view axis and preferably has a curvature of radius R about point  26  as shown in  FIG. 1 . An outer shell portion  18  is integrally formed with the arcuate wall  16 , and includes opposing side wall portions  22  and  20 , to define a noise cancellation space  12 . An exit port  24  is formed in the enclosure  10  to provide an outlet for exhaust gasses.  
         [0014]     A pipe  42  is positioned within an opening  28  formed in arcuate wall  16 . The pipe  42  provides a path for noisy exhaust gasses to enter the enclosure  10 . The pipe  42  has an inner spout portion  14  for directing the exhaust gasses toward the exit port  24 . A noise cancellation port  58  is positioned within a second opening  30  which is also formed in the arcuate wall  16 . The second opening  30  is preferably coaxial with exit port  24 . In this manner, the present invention can reduce and/or minimize any undesirable resonance of enclosure  10  by generally aligning the second opening  30  and exit port  24  relative to the exhaust gas flow.  
         [0015]     A microphone  44  is positioned near the exit port  24 . The microphone detects noise emitting from the exit port and converts the noise to an electrical signal. The electrical signal is connected to a control unit  46 . The control unit  46  has an electrical output connected to a speaker (not shown) located within speaker enclosure  50 .  
         [0016]     The enclosure  10  may be combined with a hanger assembly to facilitate mounting the noise management arrangement  1  to a vehicle (not shown). An exemplary hanger assembly is shown having first and second clamping prongs  36 ,  38  positioned on the enclosure  10 . The clamping prongs  36 ,  38  are also secured to an isolator  34 , preferably made of rubber. The isolator is clamped in an isolator mount  32  with an integral bracket  60 , which may be positioned on the underside of the vehicle.  
         [0017]     An exhaust clamp  54  is provided for attaching the exhaust component  40  to the pipe  42 . An enclosure clamp  52  is also provided for attaching a speaker enclosure  50  to noise cancellation port  58 .  
         [0018]      FIG. 2  illustrates an end view of noise management arrangement  1  as seen looking into exit port  24 . The inner spout portion  14  is visible through the exit port  24 . The inner space  12  is also visible within enclosure  10 . The exhaust acoustic output is combined with the noise cancellation acoustic output in inner space  12 . This view also illustrates the manner in which flow from the pipe  42  and flow from the noise cancellation port  58  are directed toward the exit port  24  of the noise cancellation enclosure  10 . In this embodiment, the assembly of the exhaust component  40 , active muffler  20 , speaker enclosure  50 , and noise cancellation enclosure  10  components are oriented to release exhaust from the side of the vehicle. A screen  56  may be provided for preventing debris from entering the noise cancellation port  58 .  
         [0019]     Turning to  FIG. 3 , an elevated view of the noise cancellation enclosure  10  is shown. Openings  28  and  30  are formed in an arcuate wall  16 . Curved side wall  20  extends perpendicularly from an end of arcuate wall  16  and terminates to form a portion of exit spout  24 . Side wall  22  extends perpendicularly from the opposite end of arcuate wall  16  and terminates to form another portion of exit spout  24 . A first cover portion  48  has a perimeter positioned along the side wall  22 , arcuate wall  16 , and the curved wall  20 . A segment of the first cover portion&#39;s perimeter also forms a further portion of exit spout  24 . A second cover portion  18  is in spaced relation to the first cover portion  48  and similarly has a perimeter positioned along the side wall  22 , the arcuate wall  16 , and the curved wall  20 . The segment of the second cover portion&#39;s perimeter forms the remainder of exit spout  24 . The arcuate wall  16 , side wall  22 , curved wall  16 , first cover portion  48 , and second cover portion  18  in spaced relation to the first cover portion, define a noise cancellation space  12 .  
         [0020]     For the noise cancellation enclosure  10  to provide a desirable environment for mixing sounds from the noise cancellation port  58  and the exhaust component  40 , an attempt should be made to satisfy certain dimensional relationships. Firstly, the cross sectional area of the exit port  24  should be at least 10% greater than the sum of the cross sections of the opening  28  for pipe  42  and the opening  30  for the noise cancellation port  58 . Secondly, the spatial volume of the noise cancellation space (V 12 ) less the spatial volume of the inner spout portion (V 14 ) should be greater than or equal to twice the spatial volume of the noise cancellation port (V 58 ). Stated mathematically, V 12− V 14 ≧2V 58 .  
         [0021]     The operational aspects of the noise management device will now be described. The sound of the exhaust gasses exiting from the exhaust component  40  has certain undesirable noise components. These noise components have a frequency and amplitude as is known in the art. The exhaust gasses are routed into the noise cancellation enclosure  10  via pipe  42 . The inner spout portion  14  prevents the exhaust gasses from impinging upon the side wall  22 , thereby causing an undesirable resonance which may be conducted to the vehicle via the hanger assembly. A microphone  44  placed in the proximity of exit spout  24  senses the noise and converts it to an electrical waveform, which is conducted to the control unit  46 . The noise cancellation device detects the undesirable frequency and amplitude of the noise and in response thereto creates anti-noise having an equal amplitude and frequency with an opposite phase. The noise cancellation device then sends the anti-noise waveform to a speaker located within speaker enclosure  50 . The anti-noise waves generated by the speaker are conducted through the noise cancellation port  58  and into the noise cancellation space  12 . Once the anti-noise sound waves reach the noise cancellation space  12  they destructively interfere with the noise, thereby reducing its amplitude.