FR2886338A1 - I.c. engine double-walled exhaust manifold has inner liner separated from outer wall in flange zones by insulating plugs - Google Patents

Abstract

The exhaust manifold (10), comprising an outer wall (12) with inlet (14a, 14b, 14c, 14d) and outlet (28) flanges and an inner liner (13), has plugs (17a, 17b, 17c, 17d, 19) of an insulating material, e.g. rockwool-based, between the inner liner and outer wall in the flange zones. the flanges can be moulded or cut out, and the make contact with the plugs by coupling rings (15a, 15b, 15c, 15d). In a variant of the design the gap between the lining and outer wall of the manifold can also be filled with an insulating material.

Description

The present invention relates to an exhaust manifold for an engine

internal combustion.

  An exhaust manifold serves to guide the exhaust from the cylinder head to the exhaust line and downstream equipment such as a turbocharger and / or the peripheral elements necessary for the post-treatment of flue gas. The exhaust manifold is generally equipped with several tubular branches whose inputs are each integral with an inlet flange. These branches direct, from the outlet of the different exhaust pipes of the cylinder head, the exhaust gas to a single main output integral with an outlet flange connected to the exhaust line. The exhaust manifold is most often assembled to the cylinder head by means of a screw connection which joins the inlet flanges with the exhaust face of the cylinder head. A metal seal is interposed between the cylinder head and the inlet flanges of the exhaust manifold to provide a better seal to the exhaust gas.

  More particularly, the invention relates to an exhaust manifold of the double wall type comprising an external structure provided with an inner duct in which is disposed an internal casing for guiding the gases, the external structure comprising inlet flanges and at least an outlet flange into which the inner duct and the inner casing open. In particular, it is known from US Pat. No. 4,182,112 a double-walled collector in which the internal casing disposed inside a cast iron outer structure is associated at the level of the inlet flanges with a radial flange endpiece. extending with clearance in a hollow recess made in the corresponding flange so as to limit the mechano-thermal stresses at the flange-internal tubing-nozzle arrangement after assembly of the collector on the exhaust face of the engine. This results in operation of the engine parasitic flow of exhaust gas to the space between the inner casing and the wall of the outer structure including a contact between the gas and the cast iron wall at the flange and beyond. This parasitic flow induces thermal losses at the flange and incidentally risks of deterioration of the wall exposed to the exhaust gas.

  The purpose of the invention is to provide double-walled exhaust manifolds for reducing heat losses at at least one of the flanges of the collector.

  To this end the invention is based on the use of a thermal insulator to ensure the positioning and maintenance of the inner casing of the gas guide relative to the outer structure (sheet metal walls or foundry).

  More particularly, the invention proposes an exhaust manifold of the double wall type for an internal combustion engine comprising an external structure provided with an inner duct in which an internal casing for guiding the gases is arranged, the external structure comprising flanges of inlet and at least one outlet flange into which the inner duct and the inner casing open out, characterized in that the inner casing is held in the outer structure at at least one flange, without direct contact between the inner casing and the external structure, by a plug of thermal insulation.

  Thus the invention provides an insulation of the gas guide tube relative to the fixing flanges and thermally isolates the inner casing guiding the exhaust gas with respect to the outer structure and more particularly with respect to the flanges. The invention is usable for all flanges of the exhaust manifold: flanges on cylinder head, turbo outlet flange, EGR recirculation flange. It is also applicable to all parts of the exhaust line designed on the principle of double walls (turbo, catalyst, particle filter, tube).

  In particular by eliminating any possibility of contact between the inner casing and the corresponding flange and by sealing with a thermal insulator the gap between the inner casing and the corresponding wall of the external structure, it eliminates the parasitic flow of exhaust gas and the thermal leaks that would result from a gas / wall contact of the external structure while avoiding, thanks to the nature of thermal insulation of the plug provided by the invention, new thermal leakage by conduction between the inner casing and the wall of the external structure. In addition, the wall of the inner conduit of the outer structure beyond the plug is no longer subjected to corrosive contact with the exhaust gas.

  The advantages achieved by the present invention are numerous. Among these we can mention: - The absence of direct contact between the guide tube and the outer structure (outer walls of sheet metal or cast iron, flanges) reduces the thermal losses of exhaust gases. This results in a gain in depollution.

  - The absence of contact between the gas guide tube and the cast iron reduces the risk of deterioration of the guide tube during casting of the cast iron of the molded outer structure of a molded outer wall manifold. The internal casing of gas guiding is dimensioned (thickness, material choice, ...) only according to the constraints of engine operation. This results in a gain in manufacturing cost.

  - The absence of contact between the gas guide tube and the cast iron reduces the risk of deformation of the guide tube during casting of the cast iron of the molded outer structure of a molded outer wall manifold. The portions of the internal casing adjacent the flanges are better positioned relative to the cylinder head, turbocharger, EGR. This results in a saving in space by reducing the positioning defects and a gain in engine performance by reducing the pressure drops.

  - The absence of contact between the gas and the flange reduces the thermal level of the flange and the gasket and the cylinder head. This results in an economic gain on the seal.

  - The absence of contact between the gas and the flange reduces the overall thermal level of the collector which reduces the dispersions of positioning of the elements downstream of the collector (exhaust line, turbocharger, EGR recirculation line).

  According to a preferred embodiment of the invention, the wall of the inner duct at the level of said at least one flange comprises a tubular connection in contact with said thermal insulation plug. As shown below this coupling, which can be made of steel with high resistance to high temperature exhaust gas, makes it possible to present the exhaust gas with an adequate contact surface and to protect, if necessary, the material in which it is produced. the flange.

  According to a first variant, the exhaust manifold with external structure with molded or cut flanges is characterized in that the molded or cut wall of the inner duct at the level of said at least one flange is covered by said tubular connection. It is thus possible in particular to protect the cast iron wall of the molded flanges. Advantageously, the tubular connection extends substantially to the support face of the flange to ensure good coverage by the protective plate.

  Also advantageously the collector with external structure with molded or cut flanges, is remarkable in that the tubular connection extends towards the bearing face of said flange beyond the adjacent end of the inner casing, thus avoiding in particular for the inlet flanges any interference between the flange and the exhaust face of the cylinder head.

  According to yet another embodiment of the invention, the collector comprises a molded external structure and the cavity provided between the inner duct and the inner casing is filled with a thermal insulation blanket, thereby producing a multiple plug assembly, integral with each other, each of which enters each flange to close the passage between the inner duct and the inner casing.

  According to another embodiment of the invention, the exhaust manifold comprises an outer structure mechanically welded with flanges cut and outer wall sheet metal, the tubular connection being welded to said sheet metal outer wall and the corresponding flange. It will be noted that the presence of the plugs at the flanges makes it possible to use, for the outer wall of sheet metal, an alloy exhibiting characteristics of resistance to corrosion of the lower gases compared to those of the tubular connection, hence a possible cost reduction. for the collector.

  Thus, the invention may in particular be implemented according to one of the following two general architectures: a bi-material manifold (inner casing of sheet metal, outer wall of cast iron) in which, at the flanges, a tube or fitting of protection is attached to the insulation surrounding the internal gas guiding casing. During casting, the cast iron is in contact with either the insulation or the protective tubes or connectors (the guide tubes are never in contact with the cast iron). These protective tubes surround the gas guide tube without touching it and come into contact with the molten cast iron during casting. Thus the gas guiding casing is positioned and maintained by the thermal insulator with respect to the molded structure.

  - A double wall collector made of welded sheet metal in which the inner tube for guiding the exhaust gas is positioned and maintained relative to the outer sheet by a thermal insulator.

  According to yet another embodiment of the invention, the manifold comprises tubular connectors made of sheet metal resistant to exhaust gases at high temperatures.

  According to yet another alternative embodiment of a collector according to the invention, the wall of the inner duct and / or the wall of the internal casing comprise radial projections or corrugations intended to prevent axial sliding of said plug with respect to one or to the other of said walls. This arrangement improves the seal at the plug.

  According to yet another embodiment of a collector according to the invention, the thermal insulation used is based on rockwool.

  Advantageously, the exhaust manifold according to the invention comprises alternatively a plurality of inlet flanges each equipped with a thermal insulation plug and adapted to cooperate with the exhaust face of the cylinder head of the engine. Just as advantageously the exhaust manifold according to the invention comprises alternatively an outlet flange equipped with a thermal insulation cap and adapted to cooperate with the exhaust line of the engine and / or an output flange equipped with a thermal insulation plug and adapted to cooperate with the recirculation line of the engine gases.

  According to another variant of the exhaust manifold according to the invention, the tubular connection is secured to the corresponding flange of the manifold during the casting of the molded structure. In particular for a double-walled manifold, the tubular connection or connectors are secured to said casing before casting of the molded structure but after placement of the thermal insulation on the tube.

  The invention also relates to a method for manufacturing an exhaust manifold of the double wall type defined above in all its variants, characterized in that it comprises at least the following operations: - manufacture and assembly of the elements of the internal tubing to obtain said inner casing; - Manufacturing and joining the tubular connection or connections on said inner casing after covering the inner casing with a thermal insulation; and casting of the molded cast iron or cast steel structure, the bearing surface of the concerned flange or flanges being flush with the free end of the fitting or corresponding tubular connections.

  Other characteristics and advantages of the present invention will become apparent on reading the following description presented solely by way of nonlimiting example with reference to the attached drawings in which: FIG. 1 represents a schematic view in longitudinal section of FIG. a first embodiment of an exhaust manifold of the double wall type according to the invention; FIG. 2 represents a schematic view in partial axial section of the mounting of an inlet flange of the exhaust manifold of FIG. 1 on the exhaust face of a motor yoke, accompanied by a partial enlargement showing a assembly variant of the thermal insulation plug; FIG. 3 represents a schematic view in partial axial section of the mounting of an inlet flange of a second embodiment of a double-wall type collector according to the invention on the exhaust face of a motor yoke, accompanied by a partial enlargement showing an assembly variant of the thermal insulation plug; and FIG. 4 is a diagrammatic view in partial axial section of the mounting of an inlet flange of a third embodiment of a double wall type collector according to the invention on the exhaust face of FIG. a motor cylinder head, accompanied by a partial enlargement showing an assembly variant of the thermal insulation plug.

  The double-walled exhaust manifold 10 for a four-cylinder internal combustion engine illustrated in FIG. 1 relates to an embodiment of the invention given solely by way of nonlimiting example, in this case a collector intended to be associated. to a four-cylinder cylinder head in line (not shown) at an interface represented by its projection XX 'and extending perpendicular to the plane of Figure 1. The collector 10 double wall as shown in Figure 1 is of the welded steel sheet type having on the one hand an outer structure 12 mainly consisting of an outer tubular casing 45 of relatively thin steel sheet (of a few millimeters) to form an inner conduit 11, and flanges cut in a thick steel sheet and secondly an internal casing 13 for exhaust gas flow disposed in the duct 11. In general, the steel plates are selected with high thermomechanical strength, for example austenitic steels.

  As shown in FIG. 1, the double-walled collector 10 comprises four in-line inlet flanges 14a, 14b, 14c and 14d (in accordance with XX ') in which the ends of the four inlet pipes 16a, 16b open out, 16c and 16d of the inner casing 13 disposed in the inner duct 11 (multi-branch) of the outer structure 12. Each inlet flange 14a to 14d has a central opening 18 bordered by a tubular connection 15a, 15b, 15c and 15d made of sheet metal. (preferably resistant to the corrosive action of the exhaust gas) and preferably extending to the bearing surface 21 of the corresponding flange so as to protect the wafer of the cut sheet at the level of the opening 18, the connections 15a to 15d being welded to the flanges 14a to 14d on the one hand and the external sheet metal shell 45 on the other hand. The inlet flanges 14a to 14d which extend parallel to the interface plane are intended to be secured by means of screw-nuts 23 in leaktight manner to the cylinder head 22 of the engine (see FIG. seal 24 between the bearing surfaces of the inlet flanges and the exhaust face of the cylinder head, so as to connect the inlet pipes (16a to 16d) of the manifold with the exhaust pipes 25 of the corresponding cylinders.

  The collector 10 also comprises a lateral main outlet flange (not shown and extending substantially parallel to the plane of FIG. 1 from the circularly deformed zone 27 of the envelope 45 of the structure 12) intended to be connected to the engine exhaust line (not shown), and an eccentric auxiliary output flange 26 adjacent to the inlet flange 14d, intended to be connected to the recirculation line of the engine gases (not shown) and in the center of which opens the end of the auxiliary outlet pipe 28.

  As illustrated in FIG. 1, the inner casing 13 is composed of a longitudinal central tubular portion 30 provided with middle branches 31b, 31c and lateral (not visible in FIG. 1) in which are respectively inserted by force (and possibly exceptionally welded if appropriate) the inner ends of the central inlet tubes 16b and 16c on the one hand and the main outlet tubing on the other hand (not visible in Figure 1 but whose location is represented by the hatched circle 40 ). The end inlet tubes 16a and 16d are bent and force-fitted into end pieces 33a and 33d of the longitudinal portion 30 shaped to allow axial sliding at the end pieces in the event of mechanical stresses, particularly of thermal origin, too important. Finally, the inlet pipe 16d has a branch 34 in which the auxiliary outlet pipe 28 is inserted by force (and possibly exceptionally welded if appropriate). The internal casing 13 is held in place in the pipe 11 by annular plugs of material thermal insulation, preferably based on rockwool, placed at the inlet flanges 14a to 14d (plugs 17a, 17b, 17c, 17d) and outlet flanges (plug 29 for the auxiliary outlet flange 26) of way to create between the envelope 45 of the outer structure 12 and the casing 13 a space (or cavity) of thermal insulation 36 filled with air and of substantially constant thickness.

  As illustrated in detail in Figure 2 by way of non-limiting example for the flange 14a (shown in axial section along the axis YY 'common to the opening 18, the connection 15a, the tubing 16a, the stopper 17a and at the visible end of the envelope 45), the stopper 17a is disposed in the immediate vicinity of the flange 14a between the tubular connector 15a and the free end of the inlet tubing 16a (provided slightly recessed relative to the bearing face 21 of the flange 14a), sealingly isolating the exhaust gas from the cavity 36 and the sheet of the casing 45 of the structure 12. To ensure the axial retention of the plug 14a (despite the vibrations, the thermal cycles to which the manifold is subjected and the pressure of the exhaust gas on the face 42 of the plug 17a adjacent to the bearing face 21 of the corresponding flange) and avoid any risk of unwanted sliding to impair the sealing function of the cap, this one is, o way Although advantageous, it is compressed between two complementary annular and radial corrugations 37 and 39 as shown on the partial enlargement of FIG. 2, more particularly a simple radial corrugation 37 on the tubular connector 15a and a double radial corrugation 39 on the tubing. 16a and symmetrical with respect to the corrugation 37 to maintain substantially constant the thickness of the ring of insulating material of the cap 17a after compression. The arrangement with an insulating plug described here for the flange 14a is taken over for the other flanges of the collector 10, in particular the inlet flanges 14b to 14d and the auxiliary outlet flange 26, but also for the main outlet flange. not shown.

  Moreover, without departing from the scope of the invention, the annular radial corrugations may be replaced by any means for axially holding the plugs, in particular the added components or the annular housings provided in the plates of the connections or the inlet and outlet pipes for to accommodate the lateral faces of the annual plugs.

  It should be noted that the various pipes of the inner casing 13 can slide relative to each other, especially during temperature rise of the casing due to exhaust gases. This degree of freedom makes it possible to reduce the thermal stresses in the part, because the thermal expansions of the various pipes are not upset. In addition the external structure 12 ensures the mechanical strength of the assembly of the inner casing 13 and the positioning of the collector according to the invention 10 in its environment: mounting on the motor cylinder head 22 (122) and assembly of the exhaust lines and recirculation. It will be noted that in FIG. 2 (as in FIGS. 3 and 4), the flow of the exhaust gas at the outlet of the engine cylinder head is shown schematically by an arrow in the opening 18 (118).

  The manufacture of the collector 10 can be achieved by the implementation of the method comprising the following operations: - manufacture and assembly of the elements of the inner casing (central portion 30, inlet pipes 16a to 16d, outlet pipes) to obtain the casing internal 13; covering the inner casing 13 with the insulating material in the holding zones provided for the plugs (17a to 17d, 29) - assembling and welding the outer laminations (flanges 15a to 15d, 26), tubular connections (17a-17d, etc.). ) and sheet metal casing 45 to obtain the outer structure 12; and - compressing the insulation of the plugs (17a to 17d, 29) by deforming the tubular connections and the inlet and outlet pipes of the internal casing and producing the radial corrugations 37 and 39.

  FIG. 3 illustrates the arrangement with an insulating plug of a second welded double-walled collector according to the invention (not shown) constituting a variant very close to the collector 10 and in which the only difference consists in replacing the flanges of FIG. inlet and outlet in thick sheets by thinner sheet metal flanges, in particular the inlet flange 14a of Figure 2 is replaced by the flange 14a ', the other components of the second manifold remaining substantially identical or similar to those of the manifold 10 with the same numerical references. Similarly, the manufacture of the second collector is substantially identical to that of the collector 10 described above.

  FIG. 4 illustrates the insulated plug arrangement of a double-walled bimaterial collector according to the invention (not shown) constituting another variant of the collector 10. The bi-material collector according to the invention comprises an external structure 112 molded obtained by cast iron or steel in which disposed an internal casing 113 of high temperature steel.

  Among the moldable materials used for the manufacture of collectors with external structure molded according to the invention include: - cast iron incorporating silicon and molybdenum that offer good flowability and machinability; - nickel-based cast irons (with a nickel content of at least 20%) or nickel and chromium, which offer better hot performance than silicon-based and molybdenum-based cast irons; and - for more specific applications, steels, generally of austenitic type, which offer the best performance in terms of thermomechanical behavior but are more difficult to implement in the context of cast structures.

  Once again the arrangement illustrated in FIG. 4 has many similarities with the arrangement previously described and illustrated in FIGS. 1 and 2, the identical or similar components bearing the same numerical reference increased by 100.

  With respect to the collector 10, the bi-material collector according to the invention has a cast iron outer structure 112 whose internal branches 111 carry at the inlet and outlet flanges of the tubular protective connectors made of sheet-steel exhaust gas at high temperatures, for example the connection 115a of Figure 4 mounted with screw-nuts 123 on the exhaust face of the cylinder head 122 with the interposition of a seal 124. De more thermal insulation plugs (eg 117a) disposed between the tubular connections and the end pipes (eg 116a) of the inner casing are integrated in a cover 50 of thermal insulation filling the entire cavity 136 existing between the wall molded the inner conduit 111 of the outer structure 112 and the casing 113. To ensure a good seal at the flanges and a good maintenance of the blanket 50 of insulation during the casting of the molded external structure 112, it is intended to compress the ends of the insulation forming the plugs 117a and to form the radial corrugations 137 and 139.

  The manufacture of the bi-material collector according to the invention can be carried out by the implementation of the method comprising the following operations: - manufacture and assembly of the tubular elements of the inner casing to obtain said inner casing 113; manufacture of the tubular connector (s) 115a and their attachment to the internal casing 113 once it has been covered with the cover 50 of heat-resistant insulation against melting or molten steel with the formation of radial corrugations 137 and 139 respectively on the connections 115a and the inlet pipes 116a and outlet; and casting the molded structure 112 of cast iron or cast steel, leaving free the corresponding bearing surface 121 of the flanges and avoiding the introduction and melting inside the inner casing 113.

Claims (14)

  1. Double wall type exhaust manifold for an internal combustion engine having an external structure (12, 112) provided with an inner duct in which an inner casing (13, 113) for guiding gases is arranged, the structure outer member having inlet flanges (14a, 14b, 14c, 14d, 14a ', 114a) and at least one outlet flange (28) into which the inner duct (11, 111) and the inner casing (13, 113) open out. ), characterized in that the inner casing (13, 113) is held in the outer structure (12, 112) at at least one flange (14a, 14b, 14c, 14d, 14a ', 114a), without contact direct between the inner casing and the outer structure, by a thermal insulation plug (17a, 17b, 17c, 17d, 29, 117a).   2. Exhaust manifold according to claim 1, characterized in that the wall of the inner duct (11, 111) at said at least one flange (14a, 117a).   3. Exhaust manifold according to claim 2, with external structure with molded or cut flanges, characterized in that the molded or cut wall of the inner duct (11, 111) at said at least one flange (14a, 14b, 14c, 14d, 14a ', 114a) is covered by said tubular connector (15a, 15b, 15c, 15d, 41, 115a).   4. Exhaust manifold according to claim 2 with external structure with molded or cut flanges, characterized in that the tubular connection (15a, 15b, 15c, 15d, 41, 115a) extends substantially to the face of supporting (21,121) said flange (14a, 14b, 14c, 14d, 14a ', 114a).   5. Exhaust manifold according to claim 2 with external structure with molded or cut flanges, characterized in that the tubular connection (15a, 15b, 15c, 15d, 41, 115a) extends towards the bearing face (21). 121) of said flange (14a, 14b, 14c, 14d, 14a ', 114a) beyond the adjacent end of the inner casing (13, 113).   6. Exhaust manifold according to one of claims 2 to 5 of the type with external structure mechanically welded with cut flanges (14a, 14b, 14c, 14d, 14a ', 14b, 14c, 14d, 14a', 114a). comprises a tubular connection (15a, 15b, 15c, 15d, 41, 115a) in contact with said thermal insulation plug (17a, 17b, 17c, 17d, 29, 114a) and with an outer sheet wall (45), characterized in that the tubular connection (15a, 15b, 15c, 15d, 41, 115a) is welded to said sheet metal outer wall (45) and the corresponding flange (14a, 14b, 14c, 14d, 14a ', 114a).   7. Exhaust manifold according to one of claims 2 to 5 of the molded external structure type, characterized in that the cavity (36) provided between the inner conduit (11, 111) and the inner casing (13,113) is filled by a cover (50) of thermal insulation.   8. Manifold according to one of claims 2 to 7, characterized in that the tubular connector (15a, 15b, 15c, 15d, 41, 115a) is made of sheet resistant to high temperatures.   9. Collector according to one of the preceding claims, characterized in that the thermal insulator is based on rock wool.   Manifold according to one of the preceding claims, characterized in that the wall of the inner duct (11, 111) and / or the wall of the inner casing (13, 113) comprise radial projections or corrugations (37, 39, 137). 139) for preventing axial sliding of said plug (17a, 17b, 17c, 17d, 29, 117a) relative to one or the other of said walls.   11. exhaust manifold according to one of the preceding claims, characterized in that it comprises a plurality of inlet flanges (14a, 14b, 14c, 14d) each equipped with a thermal insulation plug (17a, 17b, 17c, 17d, 29, 117a) and adapted to cooperate with the exhaust face of the cylinder head (22, 122) of the engine.   12. exhaust manifold according to one of the preceding claims, characterized in that it comprises an outlet flange equipped with a thermal insulation cap and adapted to cooperate with the exhaust line of the engine and / or a outlet flange (26) equipped with a thermal insulation plug (29) and adapted to cooperate with the recirculation line of the engine gases.   13. Exhaust manifold according to one of claims 7 to 12, characterized in that the tubular connection (15a, 15b, 15c, 15d, 41, 115a) is secured to the corresponding flange (14a, 14b, 14c, 14d , 14a ', 114a) of the collector during casting of the molded structure (112).   14. Exhaust manifold according to claim 13 taken in combination with one of claims 8 and 9, characterized in that the tubular connection (s) (115a) are secured to said casing (113) before casting of the molded structure ( 12) after placing the thermal insulation blanket (50) on the inner casing (113).   15. A method of manufacturing an exhaust manifold with external structure molded according to one of claims 13 and 14, characterized in that it comprises at least the following operations: -manufacture and assembly of the elements of the internal casing (113 ) to obtain said inner casing; manufacturing and joining the tubular connection (s) (115a) to said inner casing (113) after covering the inner casing with a thermal insulation cover (50); and casting the molded structure (112) of cast iron or cast steel, the bearing surface (121) of the concerned flange (s) (114a) flush with the free end of the connector (115a) or tubular connectors correspondents.