Abstract:
An exhaust system for a motor vehicle having a variable displacement engine includes an exhaust valve assembly that is moveable between an open position and a position blocking at least some of the exhaust gases. The blocking of some the exhaust gases increases backpressure that reflects sound waves. The reflection of sound waves provides for the conditioning of noises eminating from the exhaust system. The exhaust valve assembly utilizes an electric actuator. The exhaust valve assembly includes heat insulation features for isolating the electric actuator from heat radiating from the exhaust pipe.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention generally relates to an exhaust system for a motor vehicle having a variable displacement engine, and specifically to an exhaust valve disposed within the exhaust system for controlling noise emissions from the exhaust system.  
         [0002]     A variable displacement engine controls actuation of specific cylinders within an engine. Typically, all cylinders of an multiple cylinder engine are providing power at all times during operation of the vehicle. Under some driving conditions, power produced from all cylinders is not required to propel the vehicle. The variable displacement engine shuts down some of the cylinders to conserve fuel and increase gas mileage. During periods of low engine demand only half of the cylinders operate to propel the vehicle. The selective actuation of engine cylinders provides the most noticeable improvements in fuel efficiencies for larger vehicles with larger engines.  
         [0003]     Selective actuation of specific cylinders of an engine produces an undesirable side effect. The change in engine displacement alters sound emitted from the exhaust system. Typically larger engines are installed in larger more expensive vehicles. Consumers purchasing such vehicles have certain performance expectations. During operation of the vehicle with a reduced number of cylinders the sound emitted from the exhaust system may not convey the desired sound expected by the consumer.  
         [0004]     It is known to provide a valve within an exhaust system to reflect a portion of exhaust flow back through the engine to condition sounds from the exhaust system. Actuation of the valve is provided by a vacuum powered actuator. The vacuum powered actuator utilizes vacuum supplied by the engine through flexible hoses or tubes routed under the vehicle. The underside of a vehicle is a particularly harsh environment. Disadvantageously, the flexible hoses used to supply vacuum to the actuator become brittle and crack with age resulting in vacuum leaks and malfunction of the actuator.  
         [0005]     Accordingly, it is desirable to develop a system for conditioning noise from an exhaust system to provide a consistent desired noise from the engine regardless of changes in engine displacement with improved dependability.  
       SUMMARY OF INVENTION  
       [0006]     This invention is an exhaust system for a motor vehicle including an exhaust valve that is actuatable to block a portion of an exhaust pipe to reflect sound waves to condition sound emitted from the exhaust system.  
         [0007]     The exhaust valve of this invention includes a valve plate moveable about an axis within a valve body. The valve body is disposed within an exhaust pipe before or after a muffler. The placement of the valve body is dependent on the desired sound of the exhaust system. The valve plate is actuated by an electric actuator mounted within a housing.  
         [0008]     The housing for the actuator is supported a distance from the exhaust pipe by a valve neck. The valve neck is a tubular member having flanges at each end. The tubular configuration of the valve neck reduces the amount of thermal energy transmitted from the exhaust pipe to the housing. Electric actuators are dependable and relatively inexpensive, and are therefore more desirable than alternatively powered actuators. The reduction in thermal conduction between the valve body and the support housing prevents a substantial amount of heat from radiating to the electric actuator. The exhaust system of a vehicle produces high temperatures that present a challenge to the use of an electric actuator. It is for this reason that the exhaust valve of this invention includes features that isolate the electric actuator from thermal energy produced by the exhaust pipe.  
         [0009]     Accordingly, the exhaust valve assembly of this invention utilizes an electric actuator to provide conditioning of noise emitted from the exhaust system to provide a consistent desired sound regardless of changes in engine displacement. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows:  
         [0011]      FIG. 1  is a cut away view of an exhaust valve assembly according to this invention;  
         [0012]      FIG. 2  is a cross sectional view of the exhaust valve assembly according to this invention;  
         [0013]      FIG. 3  is a cut away view of the support housing and actuator according to this invention;  
         [0014]      FIG. 4  is a top cut away view of the exhaust valve of this invention;  
         [0015]      FIG. 5A  a top cut away view of an exhaust valve according to this invention with a rotary actuator; and  
         [0016]      FIG. 5B  is a side view of the rotary actuator.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]     Referring to  FIG. 1 , an exhaust system  10  includes an exhaust pipe  12 . Exhaust gases  16  flow through the exhaust pipe  12  after being discharged from combustion cylinders of an engine. The exhaust gases  16  resonate through the exhaust pipe  12  to emit a distinctive sound. The sound differs with the displacement of the engine. In applications where the engine provides variable displacement by selectively actuating and de-actuating cylinders depending on the driving conditions, the noise emanating from the exhaust system  10  varies in response to changes in displacement. It is desirable for sounds emanating from the exhaust system  10  to have a consistent sound regardless of the displacement of the engine. To provide this consistent sound, an exhaust valve assembly  11  is actuated to change the function of the exhaust system dependent upon engine displacement.  
         [0018]     An exhaust valve assembly  11  is disposed within the exhaust system  12 . The exhaust valve assembly  11  includes a valve body  14  that is installed within the exhaust pipe  12 . The valve body  14  houses a valve plate  24  that rotates about an axis of rotation  23  between an open and closed position. In the open position the valve plate does not block a noticeable portion of exhaust flow  16 . In the closed position, the valve plate  24  preferably blocks between 75% and 90% of the exhaust flow  16 . As appreciated, the specific amount of exhaust flow blocked by the valve plate  24  is tailored to a specific application to produce the desired consistent sound. The specific portion of exhaust flow  16  blocked by the valve plate  24  provides control of sound emitted from the exhaust system  10 .  
         [0019]     Partially blocking the flow of exhaust  16  through the exhaust pipe  12  creates an increase in backpressure. The increase in backpressure reflects sound waves back within the exhaust system  10 . Reflecting the sound waves provides for the control of sounds from the exhaust system  10 . Preferably, the sound of the exhaust system  10  is controlled to duplicate the sounds of the engine at the largest displacement regardless of the actual displacement at which the engine is operating.  
         [0020]     The exhaust valve  11  of this invention includes an electric actuator  22 . The electric actuator  22  is provided to provide the mechanical force for operation of the exhaust valve assembly  11 . As appreciated electric actuators are durable and have relatively long operational life. Further, electric actuators are easily integrated into current vehicle configurations. The electric actuator  22  is housed within a support housing  38 . The support housing  38  is spaced a distance from the valve body  14  by a valve neck  20 . The valve neck  20  includes a first flange  26  attached to the valve body  14  by bolts  28 . Between the flange  26  and bolts  28  are seals  30 . The seals  30  thermally isolate the valve neck  20  from the valve body  14 .  
         [0021]     A heat shield  18  is attached to the exhaust pipe  12  by straps  19  between the exhaust  12  and the actuator  22 . The heat shield  18  is spaced a distance from the pipe  12  to create an air space  17  ( FIG. 2 ) that aids in shielding heat from being emitted toward the actuator  22 .  
         [0022]     Referring to  FIG. 2 , the exhaust valve assembly  11  is shown in cross section such that the heat shield  18  can be seen spaced apart from the exhaust pipe  12 . The space  17  between the heat shield  18  and exhaust pipe  12  reduces radiant heat emitted from the exhaust pipe  12  toward the actuator  22 .  
         [0023]     The valve neck  20  includes the first flange  26  that is attached to the valve body  14 . The first flange  26  and bolts  28  include seals  30  disposed on either side of the first flange  26 . The seals  30  inhibit conduction of thermal energy into the valve neck  20 . The valve neck  20  includes a tubular portion  54 . The tubular portion  54  substantially reduces the amount of heat transmitted from the exhaust pipe  12  to the support housing  38 . The support housing  38  includes a plate  40  disposed between the actuator  22  and the exhaust pipe  12 .  
         [0024]     An actuation tube  32  is attached to the valve plate  24  and extends through the valve neck  20 . The actuation tube  32  is hollow and rotates about the axis of rotation  23 . Rotation of the actuation tube  32  is accomplished by linear movement of the actuator  22 . The configuration of the actuation tube  32  also inhibits transmission of heat from the valve body to the actuator  22 . The actuation tube  32  is cylindrical and hollow. Air disposed and flowing through the hollow actuation tube inhibits the transfer of thermal energy from the exhaust pipe  12 .  
         [0025]     The actuator  22  includes a first pull coil  21  and a second hold coil  25 . The first pull coil and the second hold coil  25  are of differing configurations to provide differing magnitudes of force. The first pull coil  21  provides a higher force than the second hold coil  25 . The actuator  22  must exert sufficient force to overcome pressures biasing the valve plate  24  toward the open position from the exhaust flow  16 . The first pull coil  21  produces a force to initiate movement of the valve plate  24  against the exhaust flow  16 . The second hold coil  25  produces less force than the first pull coil  21  and is of a lesser strength to utilize less power. The use of a reduced force coil provided by the second hold coil  25  is possible because maintaining the position of the valve plate  24  once the initial forces of the exhaust flow  16  are overcome are lower. A worker with the benefit of this disclosure will recognize that other actuator configuration can be used to control the valve plate  24 .  
         [0026]     Referring to  FIG. 3 , the support housing  38  encloses a clevis assembly  42 . The clevis assembly  42  links the actuator  22  with the actuation tube  32 . The actuator  22  includes a linear member  27  extendable from the actuator  22 . A spring  52  is disposed to bias the linear member  27  towards a position that causes the valve plate  24  to move to its most open position. The spring  52  provides a default position in which the exhaust valve assembly  11  will move in the event of an actuator malfunction.  
         [0027]     The clevis assembly  42  includes a clevis  44  attached to the linear member  27 . The clevis  44  moves linearly in response to movement of the linear member  27 . A lever arm  50  is attached and fixed to the actuation tube  32 . Movement of the lever arm  50  causes rotation of the actuation tube  32 . The lever arm  50  includes a slot  48 . A pivot  46  connects the clevis  44  with the lever arm  50 . The movement of the pivot  46  within the slot  48  enables radial movement of the lever  50  in response to linear movement of the linear member  27  and clevis  44 . Slot  48  is required to allow the radial movement of the lever  50  about the axis of rotation  23 . As appreciated the clevis assembly  42  is only one possible link configuration within the contemplation of this invention. A worker skilled in the art with the benefit of this disclosure would understand that other configurations for converting movement of the actuator  22  to rotation of the actuation tube  32  are suitable for use with this invention.  
         [0028]     Referring to  FIG. 4 , the valve neck  20  is shown with a first end  34  attached to the valve body  14 . A second end  36  is attached to the support housing  38 . The valve neck  20  and support housing  38  both include cross-sections  37 ,  39  disposed in a direction transverse to the exhaust pipe  12 . The cross-section  37  of the valve neck  12  transverse to the exhaust pipe is smaller than the cross-section  39  of the support housing  38  in a direction transverse to the exhaust pipe  12 . The support housing  38  includes the plate  40 . The plate  40  also acts as a secondary heat shield between the actuator  22  and the exhaust pipe  12 . This is in addition to the heat shield  18  that is wrapped at least partially around the exhaust tube  12 . The actuator  22  is partially exposed to the elements. This exposure provides some cooling benefits to the actuator  22 .  
         [0029]     Moving parts such as the clevis assembly  42  and the linear member  27  of the actuator  22  are housed within the support housing  38 . The support housing  38  encloses the clevis assembly  42  and the moving parts of the actuator  27  to prevent debris and other contaminants from fouling the system. As appreciated the exhaust system  10  is mounted to the under carriage of a vehicle. This is an especially hostile environment for most devices. The support housing  38  necessarily protects the moving parts from contamination and debris that can foul and damage the operating components of the exhaust valve assembly  11 . Although the actuator  22  is partially exposed it is shielded by the plate  40  from heat radiating from the exhaust pipe  12 .  
         [0030]     Referring to  FIGS. 5A and 5B , an exhaust valve assembly  11 ′ according to this invention includes a rotary actuator  56 . The rotary actuator  56  is attached to rotate the actuation shaft  32 . A torsion spring  58  is attached to the actuation shaft  32  to bias the rotary actuator  56  and actuation shaft  32  toward a position causing the valve plate  24  to move to the most open position. As appreciated, a worker having the benefit of this disclosure would understand that other electric actuators could be used to move the valve plate  24 .  
         [0031]     The actuator  22  is also isolated from heat emanating from the exhaust pipe  12  by the tubular portion  52  of the valve neck  20 . Isolation of the actuator  22  from heat emitted by the exhaust pipe  12  enables the utilization of the electric actuator  22 . The exhaust valve assembly  11  of this invention provides a durable, cost effective means of conditioning exhaust noises for variable displacement engines.  
         [0032]     The foregoing description is exemplary and not just a material specification. The invention has been described in an illustrative manner, and should be understood that the terminology used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications are within the scope of this invention. It is understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.