Abstract:
A passive, exhaust pressure actuated valve assembly for placement inside a tubular exhaust conduit is pivotally mounted to an off-center axle for rotation between fully closed and fully opened positions. A bias element forces the valve flap toward the fully closed position. The valve flap is shaped in a manner enabling use of the interior surface of the exhaust conduit to define stops at the full closed and full opened positions. The valve flap shape, in conjunction with the bias element arrangement, enables the flap to lie substantially parallel to a longitudinal axis of the conduit in the fully opened position, which provides for minimum back pressure in the conduit.

Description:
BACKGROUND 
     FIELD 
       [0001]    The invention generally relates to valve arrangements for vehicle exhaust systems. More specifically, the present teachings pertain to passive flapper valves for exhaust conduits. 
         [0002]    Many exhaust systems have attempted to use both active and passive valve assemblies to alter the characteristics of exhaust flow through a conduit as the exhaust pressure increases due to increasing engine speed. Active valves carry the increased expense of requiring a specific actuating element, such as a solenoid. Passive valves utilize the pressure of the exhaust stream in the conduit with which the valve is associated. 
         [0003]    Traditionally, even passive valves at their lower expense give rise to problems of unwanted back pressure when the valve is open. There is seen to be a need in the art for a passive valve arrangement which may be utilized totally inside a conduit, which is relatively inexpensive, and is capable of assuming a fully open position which minimizes unwanted back pressure. 
       SUMMARY 
       [0004]    Accordingly, an exhaust pressure actuated valve assembly for placement inside a tubular exhaust conduit includes a valve flap having first and second arcuate edges substantially conforming to curved portions of the exhaust conduit, and first and second linear edges extending between the first and second arcuate edges and providing clearance between the valve flap and an inner surface of the conduit. An axle adapted to pivotally couple the valve flap to the exhaust conduit about a longitudinal axis of the axle is coupled to the valve flap between the first and second arcuate edges such that unequal surface areas of the valve flap lie on either side of the axle. The axle further includes a protrusion at one end thereof adapted to be positioned exteriorly of the exhaust conduit. A bias element is adapted to be coupled between the exhaust conduit and the axle protrusion and is operative to bias the valve flap toward a closed position wherein the first and second arcuate edges of the valve flap contact curved portions of the exhaust conduit. Exhaust pressure may be of a magnitude overcoming a bias force of the bias element to force the valve flap to a fully opened position within the conduit wherein the first and second linear edges of the valve flap contact an inner surface of the valve conduit and are substantially parallel to the longitudinal axis of the conduit. 
         [0005]    In a further aspect of the disclosed teachings, a muffler for an internal combustion engine exhaust system includes a housing having an outer shell, input and output headers closing opposite ends of the shell and a partition inside the housing dividing it into first and second chambers. The partition has at least one aperture therethrough providing for fluid communication between the first and second chambers. A through pipe extends through the input and output headers and the partition and has a first plurality of perforations enabling fluid communication between the through pipe and the first chamber and a second plurality of perforations enabling fluid communication between the through pipe and the second chamber. A valve assembly having a valve flap is positioned inside the through pipe between the first and second pluralities of through pipe perforations. The valve flap rotates about an axle pivotally coupled to the pipe between a fully closed position wherein a first peripheral portion of the valve flap is in contact with an inner surface of the through pipe and a fully opened position wherein a plane of the valve flap is substantially parallel to a longitudinal axis of the through pipe and a second peripheral portion of the valve flap is in contact with an inner surface of the through pipe. 
         [0006]    In still a further aspect of the disclosed teachings, a fluid flow pressure actuated valve assembly for placement inside a tubular conduit includes a valve flap having a first peripheral portion adapted to be in contact with an inner surface of the conduit when the flap is in a full closed position and a second peripheral portion in contact with the inner surface of the conduit in a full open position. An axle is adapted to pivotally couple the valve flap to the conduit about a londitudinal axis of the axle, the axle coupled to the valve flap asymmetrically with respect to a surface area of the valve flap, the axle including a protrusion adapted to be positioned outside the conduit. A bias element is adapted to be coupled between the conduit and the protrusion and is operative to urge the valve flap toward the full closed position. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0007]    The objects and features of the disclosed teaching will become apparent from a reading of the detailed description, taken in conjunction with the drawing, in which: 
           [0008]      FIGS. 1A ,  1 B are respective side and end views of a valve controlling fluid flow through a conduit, the valve being in a closed position and arranged in accordance with the disclosed teachings; 
           [0009]      FIGS. 2A ,  2 B are respective side and end views of the valve of  FIGS. 1A ,  1 B in a 15° open position; 
           [0010]      FIGS. 3A ,  3 B are respective side and end views of the valve of  FIGS. 1A ,  1 B in a 30° open position; 
           [0011]      FIGS. 4A ,  4 B are respective side and end views of the valve of  FIGS. 1A ,  1 B in a fully open position; 
           [0012]      FIGS. 5A ,  5 B are respective side and end views of a first valve axle arrangement in accordance with the present teachings; 
           [0013]      FIGS. 6A ,  6 B are respective side and end views of a second valve axle arrangement in accordance with the present teachings; 
           [0014]      FIG. 7  is an end view of the valve of  FIGS. 1A and 1B  with the pipe contacting the valve flap altered to achieve substantially full blockage of the pipe when the valve is placed in the fully closed position; and 
           [0015]      FIG. 8  is a side cross-sectional view of an exhaust muffler arranged with the valve of  FIGS. 1A ,  1 B in accordance with the present teachings. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    With reference to  FIGS. 1A-4B , side and end views of a valve assembly with a valve flap in various operative positions is shown in side and end views of the conduit in which the valve assembly is positioned. Identical elements among these Figures carry the same last two designation numerals. 
         [0017]    An exhaust conduit  102  contains a snap-action valve  100  which includes a spring anchor  104 , a valve spring  106 , an external lever arm  108 , a valve flap  110 , a valve support shaft or axle  112  and a spring attachment arm  114  protruding from axle  112 . 
         [0018]    Valve flap  110  has first and second arcuate edges substantially conforming to an interior arcuate surface of conduit  102 . Flapper  110  additionally has linear side edges  116  and  118  which provide clearance  120 ,  122  between flapper  110  and an interior surface of conduit  102  when the flap is in the closed position shown in  FIGS. 1A and 1B . Bias element or spring  106  extends between an anchor point  104  on conduit  102  and attachment point  114  of external lever arm  108 . Spring  106  biases flapper  110  toward the closed positioned shown in  FIG. 1A . When in the fully closed position, flap  110  resides at an angle other than 90° to a plane extending normal to the longitudinal axis of conduit  102 . The angle of the flap with respect to a cross-sectional normal plane of conduit  102  is designated A. 
         [0019]    In operation, exhaust pressure is incident on flap  110  from the left as viewed in  FIGS. 1A-4B . When the exhaust pressure is sufficient to overcome the bias force of spring  106 , the flap  110  will start to rotate about axle  112 . The torque on valve flap  110  is determined by the bias spring force multiplied by the distance d which is the distance d between the axis of the spring and axle  112 . The spring force increases as the valve flap opens and the spring  106  stretches. However, d gets shorter as the valve continues to open resulting in the torque approaching zero as the longitudinal axis of the spring approaches an “over-center” position—i.e., as it approaches intersection with a longitudinal axis of the axle  112 . This nearly over-center positioning of the valve flap as shown at  410  in  FIG. 4A  and  FIG. 4B  results in a substantially horizontal position of the flap when in the fully open position. This positioning, in turn, minimizes back pressure in the conduit when the valve is in the fully open position. Additionally, it is to be noted that the conduit itself supplies the stop mechanism for the valve flap in both its fully closed and fully opened positions. In the fully closed position, the arcuate edges of flap  114  contact the interior surface of conduit  102  to define that position. Conversely, when in the fully opened position, as shown in  FIGS. 4A and 4B , flap  410  utilizes its lateral linear edges ( 116  and  118  of  FIG. 1B ) to come into contact with the inner surface of conduit  402  to thereby provide a stop position for the fully opened position of flap  410 . 
         [0020]    Rotating the valve flap such that the spring approaches the over-center condition also results in an easier maintenance of the valve in the fully opened position. 
         [0021]      FIGS. 5A and 5B  show a first axle arrangement suitable for use with the valve assembly disclosed herein. Valve flap  510  rotates within conduit  502  about axle  512  which is placed asymmetrically with respect to the plane of flap  510 . A bias spring  506  extends between anchor point  504  and an attachment point  514  on lever arm  508 . As seen from  FIG. 5B , axle  512  which is journaled to conduit  502  via appropriate apertures, extends only so far at its leftmost end as shown in  FIG. 5B  so as to provide clearance between the axle  512  and spring  506 . With this clearance, the spring goes to near over-center and holds that position until the exhaust flow pressure is reduced significantly. At that point, the valve flap snaps to the closed position. Lever arm  508  protrudes from axle  512  either as a separately attachable element or as an integral protrusion of axle  512 . 
         [0022]      FIGS. 6A and 6B  depict an alternative axle arrangement for use with the valve assembly disclosed. In this arrangement axle  612  extends outwardly of the conduit for a distance sufficient that it intersects the ultimate location of spring  606  when in its fully extended position. Hence, in this arrangement, spring  606  will contact axle  612  and wrap around it when the fully opened position is achieved. With this arrangement, since spring  606  wraps around axle  612 , the spring will pull the flap  610  to the closed position as soon as the exhaust flow pressure is reduced to a level unable to overcome the spring force. 
         [0023]      FIG. 7  depicts one approach to achieving nearly full closure of the exhaust conduit by the disclosed valve assembly when the valve flap is put in its fully closed position. As seen from  FIG. 7 , clearance areas such as  120  and  122  of  FIG. 1B  are substantially eliminated by flattening sides of conduit  700  such that it conforms more nearly to the overall peripheral shape of valve flap  710 . Section  724  and section  726  are flattened areas of conduit  700  to more nearly parallel the linear first and second edges of valve flap  710 . Of course it will be apparent to those skilled in the art that some clearance between the linear edges of valve flap  710  and conduit walls  724  and  726  must be present to prevent jamming of the valve flap upon rotating. 
         [0024]    An exemplary application of the disclosed valve assembly is for an automotive exhaust system muffler, such as that shown in  FIG. 8 . 
         [0025]    Muffler  800  has a housing comprised of a substantially cylindrical outer shell  818  closed at input and output ends by an input header  810  and an output header  812 . A partition  814  is attached to outer shell  818  at a position to define muffler chambers  824  and  826  on either side thereof. Partition  814  additionally includes at least one aperture  820 ,  822  enabling fluid communication between the chambers  824  and  826  inside muffler  800 . Optionally, sound absorbing material  816  may be placed in one or both interior muffler chambers. 
         [0026]    Extending through muffler  800  by passing through input header  810 , partition  814  and output header  812  is a through pipe  802 . Pipe  802  includes a first plurality of perforations  806  enabling an input section of pipe  802  to have fluid communication with the muffler chamber  824  surrounding it. Pipe  802  has a second plurality of perforations  808  at an output end enabling fluid communication from the chamber  826  surrounding it to pipe  802 . 
         [0027]    Positioned between the first and second set of perforations of pipe  802  is a valve assembly  100  arranged as previously described in conjunction with  FIGS. 1A-4B . Hence, in the closed position of valve assembly  100 , exhaust will enter muffler  800  at the input end  828  of pipe  802  as seen in  FIG. 8  and will flow through perforations  806  into the sound absorbing material  816  surrounding the pipe in chamber  824 . The exhaust then flows from the first chamber  824  to the second chamber  826  via apertures  820 ,  822  in partition  814 . Finally, the exhaust flows from the second chamber  826  through perforations  808  in through pipe  802  and out an exit end  830  of the pipe  802  as seen from  FIG. 8 . 
         [0028]    When the exhaust pressure is high enough to overcome the force of bias spring  106 , the valve flap  110  will open to a nearly horizontal position within pipe  802  to essentially have most of the exhaust gas bypass the first and second chambers and their associated sound absorbing material. Since the flap  110  will be substantially horizontal in  FIG. 8  in the fully open position, back pressure in muffler  800  is minimized. 
         [0029]    The invention has been described in conjunction with a detailed description of embodiments disclosed for the sake of example only. The scope and spirit of the invention are to be determined from an appropriate interpretation of the appended claims.