Patent Publication Number: US-6668973-B2

Title: Transverse partition for exhaust volume

Description:
The present invention relates to a transverse partition for separating an exhaust volume into two adjacent chambers, the partition being of the type comprising at least one passage for allowing gas to flow between the two chambers, the gas flow section through the passage being modifiable under drive from the difference between the pressures on the two sides of the partition. 
     BACKGROUND OF THE INVENTION 
     In exhaust mufflers, it is known to define two adjacent chambers that are separated by a transverse partition, the chambers being capable of being put into communication with each other automatically at high engine revolutions. 
     For this purpose, a flap valve is installed on the transverse partition extending across the exhaust muffler and separating the two adjacent chambers. 
     By way of example, such a valve is described in Japanese patent application JP-08004990. That valve comprises a seat defining a gas flow passage and a flap hinged to an edge of the seat. The flap can be moved between a closed position where it bears against the seat and a position in which it is spaced apart from the seat allowing gas to flow freely. A spring is provided to urge the flap towards its closed position. The flap is moved away from the seat under drive from the difference between the pressures in the two chambers. 
     The valve structure described in that document is very complex and it incorporates a large number of parts, thereby considerably increasing the cost of manufacturing an exhaust muffler that incorporates it. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     An object of the invention is to propose a transverse partition for an exhaust volume that allows gas to pass through in controlled manner and that can be manufactured at very low cost, and also to propose an exhaust muffler incorporating it. 
     To this end, the invention provides a transverse partition of the above-specified type for separating an exhaust volume into two adjacent chambers, the partition comprising a wall pierced by at least one slit defined between two adjacent edges of the wall, which wall is elastically deformable under drive from the pressure difference between the two sides of the partition, between a rest position in which wall continuity is ensured, the two edges of the slit being substantially touching, and a deformed position in which the two edges of the slit are spaced apart so as to define said gas flow passage between them. 
     In particular embodiments, the partition includes one or more of the following characteristics: 
     said wall is generally plane; 
     said slit is generally spiral-shaped; 
     said wall is generally cylindrical; 
     said slit is generally helically shaped; 
     said generally cylindrical wall is closed at one of its ends; 
     the partition comprises a generally plane main panel, and said generally cylindrical wall extends perpendicularly to said panel; 
     one of the surfaces of the generally cylindrical wall is covered by a gas-permeable sheath, in particular a braid; 
     said slit is wound around at least two turns; 
     the thickness of the region of the wall in which the slit is defined is greater than the average thickness of said partition; and 
     the thickness of the wall region where the slit is defined is greater than the average thickness of said partition. 
     The invention also provides an exhaust muffler defining an enclosure and including at least one transverse partition as defined above, said partition defining two adjacent chambers within the enclosure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood on reading the following description given purely by way of example and made with reference to the drawings, in which: 
     FIG. 1 is a perspective view of an exhaust muffler of the invention; 
     FIG. 2 is a perspective view of the intermediate partition of the FIG. 1 muffler, the partition being shown at rest; 
     FIG. 3 is a view analogous to FIG. 1 showing the same intermediate partition, the partition being shown elastically deformed under drive from a pressure difference between its two faces; 
     FIG. 4 is a perspective view of a variant embodiment of the intermediate partition, the partition being shown at rest; and 
     FIG. 5 is a perspective view of the FIG. 4 partition shown deformed under drive from a pressure difference between its two faces. 
    
    
     MORE DETAILED DESCRIPTION 
     The exhaust muffler shown in FIG. 1 comprises an exhaust volume  12 , a gas feed tube  14 , and a gas exhaust tube  16 . The volume  12  comprises a generally cylindrical case  18  closed at each end by an end wall  20 ,  22 . The tubes  14  and  16  pass through the end walls  20  and  22  and project into the inside of the exhaust volume. 
     The volume  12  also has an intermediate partition  24  extending transversely and defining two adjacent chambers  26  and  28  inside the volume  12 . 
     Such a transverse partition can also be referred to as a “cup”. 
     FIG. 2 shows the partition  24  at rest. It comprises a plane main wall  30  in the form of a disk surrounded by a peripheral rim  32  enabling the intermediate partition  24  to be secured to the casing  18  of the exhaust volume. 
     The main wall  30  is pierced by two openings  34 ,  36  each serving to pass one of the tubes  14  and  16 . Thus, each tube passes through the intermediate partition  24  and opens out into a chamber of the exhaust volume after passing right through the adjacent chamber. 
     The running portions of the tubes  14  and  16  are provided with side slots  38  that open out into the chambers which they pass right through. 
     In its central region, the main wall  30  is pierced by at least one slit  40  made in an elastically deformable region of the wall. 
     The region where the slit  40  is formed can be of thickness that is different from the average thickness of the wall  30 , which in this example means the major portion of the partition. Advantageously, the thickness of the region where the slit is formed is greater than the average thickness of the wall. The values of these thicknesses can lie in the range 0.4 millimeters (mm) to 2 mm. For example, the wall  30  can be made of steel. The thickness of the wall in the region where the slit is formed can be 1 mm while its thickness outside the region in which the slit is formed can be 0.5 mm. 
     In an embodiment that is not shown, the region where the slit  40  is formed can be constituted by an extra part. This part is secured to the wall  30  by any means of appropriate type, e.g. rivets. 
     In the embodiment shown in FIG. 2, the slit  40  is generally spiral shaped. It is wound over about five turns. The slit is wound advantageously over more than one turn. The slit  40  thus defines a spiral-shaped strip  42  in the central portion of the wall  30  and extended in its central portion by a disk  43  formed integrally therewith. 
     Advantageously, the slit  40  is made by laser cutting. It could also be formed by punching. 
     The slit  40  is of small width, such that the two edges defining the slit lie in the immediate vicinity of each other when the partition  24  is at rest, i.e. when it is not being stressed by a difference in pressure between its two faces. Under such conditions, the spiral shape  42  lies in the main plane of the wall  30  thus forming a substantially solid screen presenting very little leakage between the two chambers of the exhaust volume, with the edges of the slit  40  then being substantially adjacent. 
     In contrast, when a significant pressure difference exists between the chambers  26  and  28 , the spiral strip  42  is stretched by elastic deformation as shown in FIG.  3 . The strip deforms in a direction that is substantially perpendicular to the plane of the wall  30 . The edges defining the slit  40  are then spaced apart leaving between them a passage  44  that allows gas to flow from one chamber to the other. 
     Once the pressures in the two chambers  26  and  28  have come into equilibrium, the elastically deformed region of the wall returns to its position shown in FIG. 2 under drive from the elasticity of the spiral shape  42 . In this position, continuity of the solid wall  20  is provided. 
     In another variant, resilient means are associated with the spiral strip  42  so as to assist it returning to its initial position once pressure has moved into equilibrium. Advantageously, the resilient means are constituted by a spring having one end secured to the disk  43  and a second end secured to the end wall  22 . The person skilled in the art can define suitable characteristics for the spring, and in particular its stiffness. In this embodiment, the spring is sheltered from the high temperature gas flow and serves to guarantee increased lifetime for the device of the invention. 
     It will be understood that using a deformable region defined by a slit through the wall  30  makes it possible to ensure that gas flows in controlled manner between the two chambers, with such flow being possible only if a sufficient pressure difference exists between the two chambers. In addition, this gas flow control can be obtained at a manufacturing cost that is very low since there is no need to add any particular elements into the exhaust volume. 
     FIGS. 4 and 5 show another embodiment of a transverse partition  124  that can be implemented in the exhaust muffler of FIG. 1 by replacing the intermediate partition  24 . In this embodiment, elements which are identical or analogous to those of the embodiment shown in FIGS. 2 and 3 are given the same reference numerals plus  100 . 
     Thus, the transverse partition  124  has a main panel  130  in the form of a disk with a surrounding rim  132  and it is provided with two openings  134  and  136  for passing tubes  14  and  16 . In its central portion, the panel  130  has a third opening of circular section  150  with a tube  152  fitted to the perimeter thereof, which tube is defined by a cylindrical wall  154 . The tube  152  is of circular section. In a variant, its circular section could be of varying radius or its section could be elliptical. It presents an axis X—X extending perpendicularly to the panel  130 . The tube is made of an elastically deformable material, e.g. a steel of the Inconel (registered trademark) type or a stainless steel having a thickness of 0.8 mm. In contrast, the thickness of the main panel  130  is 0.5 mm. 
     The tube  152  is crimped at one end to the surface of the panel  130 . Thus, it extends on one side only of the panel  130 . At its free end, the tube  152  is closed by a stopper  156  which is constituted in this case by a disk welded thereto. 
     Over the major part of its length, the cylindrical wall  154  presents a slit  160 . This slit is helically shaped. It extends over some number of turns that is greater than two, and which is equal to twelve, for example. The slit thus defines turns  162  along the tube. 
     At rest, as shown in FIG. 4, the edges defining the slit  160  are touching so that the wall  154  defines a continuous surface forming an essentially gastight barrier between the two chambers of the exhaust muffler. The turns  162  then touch one another. 
     In contrast, when the pressure in the chamber communicating with the inside of the tube  152  increases, then the wall  154  expands under elastic deformation and the initially touching edges of the slit  160  move apart from one another so as to define a gas flow passage  164  which is helical in shape. The turns  162  are then no longer touching. 
     After pressure has returned to equilibrium in the two chambers, the cylindrical wall  154  returns to its initial shape under drive from the elasticity of the wall  154 . The turns  162  defined by the slit  160  are then touching. 
     In a variant, a gas-permeable sheath  166  is fitted over the major fraction of the surface of the tube  152  in contact with one and/or the other of the surfaces of the cylindrical wall  152 . In an additional variant (not shown), the sheath  166  is fitted to the surface of the turns  162 . By way of example, the sheath can be made of a metal braid or a composite material braid. Such a sheath is represented by chain-dotted lines in FIGS. 4 and 5. 
     The presence of this sheath reduces the noise that results from gas flowing in the tube. 
     In an additional variant, resilient means are associated with the tube  152  for assisting it back into its initial shape after pressures have returned to equilibrium. Advantageously, the resilient means are constituted by a spring secured via a first end to the stopper  156  and via its second end to the end wall  22 . The person skilled in the art knows how to define suitable characteristics for the spring, and in particular its stiffness. In this embodiment, the spring which is sheltered from any high temperature gas flow serves to provide longer lifetime for the device of the invention.