Abstract:
This exhaust manifold comprises: an outer envelope comprising: at least one flange connected to the outer shell and having at least one gas circulation port, the outer envelope having at least one gas circulation port; at least one internal duct ( 31 ) arranged inside the outer envelope and opening via a gas circulation port, characterized in that: the or each internal duct ( 31 ) is formed, at least for the most part of its length, of a ceramic material and is engaged through the or each port; and it comprises an annular diaphragm ( 34 ) that is impermeable to the gases but radially and axially elastically deformable and positioned around the or each internal duct ( 31 ), between the or each internal duct ( 31 ) and the outer envelope ( 18 ), the diaphragm ( 34 ) being connected at its periphery to at least one out of the outer envelope ( 18 ) and the or each internal duct ( 20, 31 ).

Description:
The present invention relates to an exhaust manifold for an exhaust line of an internal combustion engine, of the type comprising: 
     an outer envelope comprising: 
     at least one flange connected to the outer shell and having at least one gas circulation orifice, the outer envelope having at least one gas circulation orifice; 
     at least one internal duct arranged inside the outer envelope and opening via a gas circulation orifice. 
     BACKGROUND OF THE INVENTION 
     Vehicles with heat engines are nowadays equipped with exhaust lines that include pollution control members such as catalytic purification members and/or particle filters. In order to permit satisfactory operation of such pollution control members it is necessary for the exhaust gases to reach them at a high temperature. It is therefore expedient to avoid too great a loss of heat in the exhaust line and especially in the manifold separating the outlet of the heat engine from the first pollution control member. 
     Various solutions have been envisaged to that end. In particular, manifolds comprising internal ducts maintained in an outer shell separated from the internal ducts by an air space or an insulating material are found to be effective in avoiding too great a loss of heat. 
     Such manifolds comprise a flange for fixing to the cylinder head of the engine, on which there come to bear on the one hand the internal ducts and on the other hand the outer shell. An outlet flange is also fixed to the outer shell, allowing the remainder of the exhaust line, and especially the turbocompressor, to be assembled. 
     Tightness for that type of assembly is ensured by the tight welding of the outer shell to the cylinder-head flange and the outlet flange. 
     The object of the invention is additionally to achieve satisfactory tightness between the internal ducts and the flanges, especially the outlet flange. 
     Such tightness is necessary when a material is used between the internal ducts and the outer shell, especially in the case of insulating materials or holding elements based on ceramics fibres, in order to prevent all or some of the material from being sucked in either by the engine or by the exhaust line, and especially the turbocompressor. 
     Connection and tightness between the internal ducts and the flanges are tricky to achieve because of the differential expansions, especially axial expansions, that are noted between the internal ducts and the outer shell. It is in fact impossible to connect the outer shell and the internal ducts rigidly to the cylinder-head and outlet flanges. 
     The object of the invention is to propose an exhaust manifold having a satisfactory connection and satisfactory tightness between the internal ducts and the outlet flange. 
     Tightness in the region of the cylinder-head flange is in that case assumed to be satisfactory and the connection with the flange is considered to be rigid. 
     The invention therefore proposes to achieve satisfactory tightness on the outlet flange side without imposing a rigid connection between the internal ducts and that flange. 
     SUMMARY OF THE INVENTION 
     This invention relates particularly to exhaust manifolds in which the internal ducts are brought together in a tight manner especially in a single outlet duct. However, it is possible to keep the ducts separate as far as the flange by adding a sealing element between the various ducts by adhesive bonding, for example, or with the aid of a gasket. 
     To that end, the invention relates to a manifold of the above-mentioned type, characterized in that: 
     the or each internal duct is formed, at least over the main part of its length, of a ceramics material and is engaged through the or each orifice; and 
     it comprises an annular diaphragm which is impermeable to gases and is radially and axially deformable in a resilient manner and which is arranged around the or each internal duct between the or each internal duct and the outer envelope, the diaphragm being connected at its periphery to at least one of the outer envelope and the or each internal duct. 
     According to particular embodiments, the manifold has one or more of the following characteristics: 
     the outer envelope comprises an outer shell and a flange which is connected to the outer shell and delimits the or each gas circulation orifice; 
     the diaphragm is connected at its periphery to the other of the flange and the or each internal duct; 
     the diaphragm is resiliently pressed, at its periphery, against the other of the flange and the or each internal duct; 
     the diaphragm comprises, on the one hand, a skirt having an annular region for connection to the other of the flange and the or each internal duct and an annular profile for abutment on the other of the flange and the or each internal duct and, on the other hand, a resilient, radially acting member which is pressed against said annular profile in order to hold it, under radial stress, against the other of the flange and the or each internal duct; 
     the resilient member comprises a resilient ring which encircles said annular profile and presses it, by an action directed towards the centre, against the internal duct; 
     the resilient member encircling said annular profile exerts an action directed towards the centre on the annular profile against the internal duct, the intensity of which action is less than that of the discharge pressure of the space between the internal duct and the outer shell; 
     said profile defines an annular channel which is open to the outside and contains said resilient member; 
     said channel has two converging edges which delimit an opening whose width is less than the maximum width of the channel; 
     the diaphragm is in the form of a bellows; 
     the diaphragm is generally tapered; 
     the diaphragm comprises one or more discharge vent(s); 
     the diaphragm is connected by welding; 
     at least part of the space delimited between the outer shell and the or each internal duct contains a filling material; and 
     the diaphragm is connected at its periphery to the outer envelope. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood upon reading the following description, which is given solely by way of example and with reference to the drawings, in which: 
         FIG. 1  is a top view, partially cut away, of an exhaust manifold according to the invention associated with the outlet flange; 
         FIG. 2  is a cutaway view of the detail of the connection of the exhaust manifold and the outlet flange; and 
         FIG. 3  is a view identical with that of  FIG. 2  of a variant of the manifold and of the outlet flange. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a heat engine  10  coupled to an exhaust manifold  12 . The heat engine comprises, for example, four cylinders, each of which has an associated valve duct  14  forming an exhaust outlet provided through a cylinder head  15  of the engine. 
     The four outlets  14  open in the same plane  16  of the cylinder head, to which plane the inlet of the exhaust manifold  12  is fixedly joined. 
     The manifold  12  substantially comprises a tight outer envelope  18  in which there are accommodated four tubes  20  forming internal ducts for evacuating the exhaust gases. Each tube is associated with an exhaust outlet of a cylinder of the heat engine  10 . 
     A holding material and/or a heat-insulating material, formed especially by a layer of ceramics fibres, fills at least part of the space  21  delimited between the envelope  18  and the tubes  20 . 
     The envelope  18  comprises an outer shell  22  which surrounds the totality of the tubes  20 , a flange  24  for connecting the manifold to the cylinder head  15  of the engine, and an outlet flange  25  which serves to connect the manifold to the remainder of the exhaust line and especially to a turbocompressor. 
     The outer shell  22  is formed, for example, by two metal half-shells which are joined together by a median peripheral weld. The shell defines a profile which converges from the flange  24  towards an end equipped with the outlet flange  25 . 
     The flange  24  is formed by a solid plate which has four inlet orifices  24 A arranged opposite the evacuation outlets  14  of the engine. It further comprises holes for the passage of screws for fixing the manifold to the cylinder head. 
     Each tube  20  passes through the flange  24  over substantially its entire length through an orifice  24 A. 
     The outlet flange  25  has a main outer face which forms a surface for abutment  25 A especially on the turbocompressor and an opposing inner surface  25 B, between which there is formed a through-orifice  27 . The outer shell  22  is fixed to the inner surface  25 B by an external weld  28 . 
     The internal tubes  20  are formed of a ceramics material, for example those described in patent applications U.S. Pat. No. 6,134,881, U.S. Pat. No. 6,161,379, U.S. Pat. No. 6,725,656 and WO-2004/106705. Those materials comprise a composite matrix which is based on inorganic polymer and reinforced by fibres, preferably ceramics fibres. Such materials are particularly suitable owing to their low thermal inertia, their low thermal expansion as compared with metal, especially a stainless steel, their mechanical properties, which allow them to withstand the flow of hot gases present in the exhaust and the vibrational stresses characteristic of motor vehicles, and, finally, owing to their high-temperature resistance in respect of the hot gases leaving an internal combustion engine. 
     The thickness of the tubes  20  in their functioning portion is from 0.4 to 1.2 mm. They converge towards one another from the inlet orifices  24 A of the manifold, each corresponding to one cylinder, to form a bundle of tubes opening in the region of the outlet flange  25  of the manifold through a substantially tubular section  30  forming the outlet of the envelope. 
     The tubes  20  are preferably independent of one another over their entire length. Accordingly, they are disposed contiguously in the outlet section  30 . They all open in the same plane transverse to the section  30  in the region of their downstream end. At that end, each tube has a quarter-disk-shaped cross-section. 
     However, the tubes can come together beforehand in a forked section, thus forming a one-piece bundle leading to a single outlet orifice. 
     The four tubes  20  open in the same converging section made of ceramics, forming an outlet duct  31 . 
     The four tubes and the outlet duct  31  are, but do not necessarily have to be, maintained in the radial position in the section  30  by a seal  32  formed by a ring made of a metal lattice. 
     The duct  31  extends through the orifice  27  and opens in the thickness of the flange  25 . 
     Advantageously, and as is shown in  FIG. 2 , a diaphragm  34  that is impermeable to gases and is radially and axially deformable in a resilient manner is interposed between the outlet duct  31  and the outlet flange  25 . The diaphragm  34  thus surrounds the duct  31  and is connected to at least one of the flange  25  and the outlet duct  31 . In the embodiment shown in  FIG. 2 , the diaphragm  34  is connected, for example, by adhesive bonding to the outer surface of the outlet duct  31 . To that end it has an end collar  36 . Likewise, the diaphragm is, for example, welded to the inner planar surface  25 B of the flange outside the associated orifice  27 . To that end it comprises a skirt  38  which is pressed against the inner surface of the flange. 
     The end of the diaphragm  34  that is connected to the outlet duct  31  is disposed at a distance from the flange  25  and the orifice  27 . 
     The diaphragm  34  advantageously has a generally tapered wall converging from the flange  25  towards the outlet duct  31 . Preferably, the tapered wall is in the form of a resiliently deformable bellows having a succession of tapered surfaces which are offset angularly and are connected to one another in the manner of an accordion. 
     For example, the bellows is formed by a stamped metal sheet having a reduced thickness of the order of from 0.1 to 0.2 mm. 
     While remaining generally tight, the diaphragm advantageously has a calibrated discharge vent which allows excess pressure in the inter-wall space  21  to be avoided. The vent is of such a size as to allow the air to circulate while preventing any fibres from being sucked in outside the inter-wall space and especially towards the engine or the turbocompressor. 
     The diaphragm  34  ensures tightness on the one hand between the exhaust line, and especially the turbocompressor, and the flange  25  and on the other hand between the flange  25  and the outlet duct  31 . Accordingly, the exhaust gases do not circulate in the inter-wall space  21  delimited between the ducts  20  and the outer envelope  22 . 
     Because the tubes  20  are made of ceramics material, they are subject to very small expansions, which permits very precise adjustment between the tubes and the outlet flange. 
     In addition, because the ceramics constituting the tubes  20  is a good heat insulator, very little of the heat of the exhaust gases is transferred to the solid flange  25 , ensuring that the majority of the heat is guided through the manifold, thus permitting satisfactory operation of the pollution control members located downstream of the manifold, such as a catalytic purification member or a particle filter. 
       FIG. 3  shows a variant of the coupling between the flange  25  and an outlet duct  31 . In this embodiment, the diaphragm, which is denoted by reference numeral  44 , is connected to the flange  25  along its inner surface  25 B and is only pressed resiliently in contact with the outer surface of the outlet duct  31 . To that end, the diaphragm  44  comprises a metal skirt  46  having an annular connecting region  48  pressed against the inner surface of the flange  25 , and an annular profile  50  for abutment on the outer surface of the outlet duct  31 . The cross-section of the skirt  46  is generally in the shape of a cross or a question mark. 
     The annular profile  50  delimits a channel  52  which opens on the outside opposite the associated outlet duct  31 . The channel  52  has converging edges  54 , so that the width of the opening of the channel is smaller than the maximum width of the channel  52 . 
     An annular resilient member  56  formed by a resilient ring is accommodated and maintained inside the channel  52 . The resilient member  56  is capable of pressing the bottom of the channel  52  against the outer surface of the outlet duct  31  by exerting a force directed towards the centre on the annular abutment profile. 
     The resilient ring  56  is formed, for example, by a metal lattice and has, when at rest, a diameter smaller than the outside diameter of the outlet duct  31 . 
     In the vicinity of its inner surface, the flange has a counterbore  58  which locally widens the orifice  27 . The annular abutment profile  50  and the resilient ring  56  are partially accommodated in the counterbore by being pressed against the outer surface of the outlet duct  31 . 
     In order to hold the diaphragm  44  in position, the annular region  48  is welded at its outer periphery to the inner surface  25 B of the flange by a weld line  60 . 
     As in the preceding embodiment, the arrangement described here ensures, in view of the fact that the abutment profile  50  is held pressed against the outer surface of the outlet duct  31 , tightness between the inside and the outside of the envelope of the manifold. However, if there is excess pressure in the manifold, the diaphragm  44  is deformed resiliently in the manner of a centrifuge, allowing the gas that resulted in the excess pressure to escape between the outlet duct  31  and the diaphragm. 
     To that end, the resilient ring  56  is such that it exerts an action directed towards the centre against the internal duct, the intensity of which action is less than that of the discharge pressure of the space between the internal duct and the outer shell. 
     In a different embodiment, the diaphragm  34  is fixed to the outer shell  22  rather than to the flange  25 , especially in the case of an embodiment without a flange. 
     In another embodiment, the assembly of the outer envelope  22  is not necessarily tight. The half-shells are, for example, assembled by means of a discontinuous median peripheral weld, ensuring only mechanical holding. The same is true of the assembly of the cylinder-head flange  24  and the outlet flange  25  on the outer envelope  22 . 
     Those different mounting solutions produce particularly advantageous solutions in terms of the tightness of the manifold. 
     In particular, the holding or insulating material disposed in the inter-wall space is protected.