FR2889559A1 - Internal combustion engine`s exhaust manifold for guiding exhaust gas, has molded external structure with inlet and outlet flanges, and space between tubes and pipes are filled by covering heat insulating material - Google Patents

Abstract

The manifold (10) has a molded external structure (12) provided with inlet pipes (14a, 14b) joined to form an outlet pipe (16). An inner tube (18a, 18b) for guiding of gas is arranged inside each of the pipes leaving a space between the tubes and the corresponding pipes. The structure has an inlet flange (24a, 24b) in which the inlet pipe and inner tube are opened, and an outlet flange (30) in which the pipe (16) and tube are opened. A space between the inner tubes and the inlet pipes are filled by covering of heat insulating material integrated with a mold of the structure.

Description

Exhaust manifold for internal combustion engine

  The present invention relates to an exhaust manifold for an internal combustion engine and more particularly to an exhaust manifold of the double-wall type and long separate ducts for internal combustion engine.

  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.

  The collectors are therefore, by their function, subjected to important vibratory and thermomechanical stresses, especially the long and separate duct collectors in which the tubular branches form a fan structure. A first problem encountered in the case of collectors is therefore their thermomechanical and vibratory behavior.

  Moreover, the heat losses caused by exchanges with the collector wall is a second problem related to these exhaust manifolds, in that they affect the efficiency of the exhaust gas pollution control downstream of the collector.

  Finally, a third difficulty related to the use of exhaust manifolds is related to their superficial oxidation, which causes the appearance of a phenomenon of desquamation.

  It is known, for solving these problems, to produce mechanically welded double wall exhaust manifolds. In these collectors, the external structure is made by stamping thin sheets which are then welded.

  However, these welded double wall exhaust manifolds are difficult to design and make reliable. However, regarding heat losses, a poorly designed welded double wall exhaust manifold may be less effective than a single wall exhaust manifold. In addition, the welded double-walled exhaust manifolds are relatively expensive and impose many welds which are a source of a large part of nonconformities welded double-walled exhaust manifolds and many failures during their use .

  Furthermore, it is known double wall collectors whose outer structure is made by molding around a sand core disposed around the inner casing. This core of sand must therefore be evacuated thereafter, before the commissioning of the collector, through a grit hole, this additional step causing a loss of time in the manufacturing process and additional manufacturing cost.

  On the other hand, document US 4 182 122 discloses an exhaust manifold for a thermally insulated internal combustion engine inside so as to keep the temperature of the external structure lower than a predetermined temperature. To do this, the exhaust manifold according to US 4 182 122 comprises an inner casing composed of a plurality of nested elementary tubes which can slide axially with respect to each other, a seal being arranged between the elementary tubes in such a way that to allow axial expansion or contraction of the elementary tubings. An insulative body is molded or cast to fit around each elemental tubing so as to leave a stream of air between the inner face of the insulating body and the outer surface of the inner casing. In order to avoid the appearance of blisters on the external structure, a fibrous casing of reduced thickness is surrounded around the molded insulating body. The outer structure is then molded or cast directly around the assembly formed by the inner casing, the insulating body and the fibrous casing.

  Although this manifold corrects some defects in the welded double-walled exhaust manifolds, it still has a number of disadvantages. Among these, it can be mentioned that the insulating body must be molded before being put in place, which adds a step to the manufacturing process of such a collector.

  In addition, nested tubing technology is only suitable for short duct type manifolds with a single vent and can not be applied to long, separate duct manifolds.

  The object of the invention is therefore to provide an exhaust manifold of the double-walled and long-pipe type separated for an internal combustion engine which corrects the above-mentioned defects, in particular being able to be achieved more rapidly and with good reproducibility while ensuring good thermal insulation between the internal pipes and the external structure.

  This object of the invention is achieved by means of an exhaust manifold of the double-wall type and long separate ducts for internal combustion engine remarkable in that it comprises: a molded external structure provided with several ducts; inlet joining to form at least one outlet duct, - an internal gas guiding manifold disposed within each of said inlet ducts leaving a space between said inner duct and said corresponding inlet duct, the structure external device comprising inlet flanges into which said inlet ducts and said internal pipes open, and at least one outlet flange into which said at least one outlet duct and said internal ducts open, said space between said internal ducts and said ducts; inlet or outlet ducts being filled by a thermal insulating material coating forming an integral part of the molding core of the structure external re.

  As will be seen in more detail in the remainder of the description, the advantages obtained by virtue of the present invention with respect to the known exhaust manifolds are numerous. Among these we can mention: - The removal of the sand core allows a significant gain on the manufacturing cost.

  The possibility of having a molded external structure makes it possible, on the one hand, to eliminate the weld beads which pose reliability problems and, on the other hand, to greatly reduce the geometrical dispersions of the finished exhaust manifold.

  - The price of raw material and foundry processes reduce the manufacturing costs of the exhaust manifold.

  - The molded external structure offers a better behavior to vibratory stresses.

  - The outer structure is thus protected from oxidation by the internal pipes.

  - A reduction of the temperature of the outer wall with an economic advantage since we can remove the heat shield.

  - The internal pipes are independent of each other, especially during the temperature rise of the room due to the exhaust gas. This degree of freedom makes it possible to reduce the mechanical stresses in the part, because the thermal expansions of the various pipes are not upset.

  Preferably, near said at least one outlet flange, said inner tubes are encircled by a steel sleeve, separating said internal tubes from said at least one outlet duct.

  Thus, advantageously, the internal tubings of said outlet duct are thermally insulated.

  Preferably, said steel bushing is mounted, with a gap of expansion, between said internal pipes and said at least one outlet duct.

  Thus, advantageously, the internal tubes are able to expand near the outlet flange independently of one another. This avoids the appearance of mechanical stresses inside the internal pipes near the outlet flange of the collector.

  Preferably, said coating of thermal insulating material is of fibrous material, more preferably said thermal insulating material comprises rock wool.

  Thus, advantageously, this material resists molten iron well and is able to fulfill its core function during the molding of the external structure while having good thermal insulation properties.

  Preferably, at their end oriented towards said inlet flanges, said internal tubes are disengaged from said coating of thermal insulating material.

  Preferably, at their end facing said inlet flanges 30, said internal pipes are mounted in the external structure with an expansion gap.

  The invention also relates to a method of manufacturing an exhaust manifold as described above in all its variants, remarkable in that it comprises at least the following operations: a) Manufacturing the various internal tubes; b) Covering each internal tubing separately or all of the internal tubing with a coating of thermal insulating material; c) Installation of the internal tubing assembly and the coating of thermal insulating material; and d) casting or molding the outer structure.

  Thus, the method according to the invention allows significant time savings since it is no longer used molding sand cores, they must be removed before commissioning the collector.

  Preferably, the manufacturing method further comprises, between operations a) and c), before or after operation b), the following operation e) e) setting up a socket at the outlet tubing.

  Preferably, internal tubings are made longer than necessary so as to ensure correct positioning of said inner tubes in said mold and in that the excess parts of the internal tubings are removed after the casting of said external structure.

  Thus, advantageously, the introduction of internal tubing is facilitated as well as the molding of the external structure.

  Other advantages and features of the invention will emerge from the description which follows, presented solely by way of illustrative and non-limiting example, with reference to the appended figures, in which: FIG. 1 represents a diagrammatic view of longitudinal section a double-walled double-duct exhaust manifold separated according to the invention, - Figure 2 shows a side view of the external structure of an exhaust manifold with four separate long ducts according to the invention, and FIG. 3 represents a side view of a set of four internal tubes suitable for being mounted in the external structure shown in FIG. 2.

  The double-walled and two separate long-pipe exhaust manifold for two-cylinder internal combustion engine shown in FIG. 1 is intended to be associated with a two-cylinder in-line cylinder head (not shown) at the level of an interface represented by its projection XX 'and extending perpendicularly to the plane of FIG.

  The exhaust manifold 10 with double wall and long separate ducts comprises, as shown diagrammatically in FIG. 1, an external structure 12, produced by molding, the function of which is to ensure the mechanical strength of the collector 10 and the setting in the position of the collector 10 in its environment. This external structure 12 forms two long and separate inlet ducts 14a, 14b joining in an outlet duct 16, an internal duct 18a, respectively 18b, being disposed inside the inlet duct 14a, respectively 14b, the two internal pipes 18a, 18b extending inside the outlet duct 16. The internal pipes 18a, 18b are made in one piece, by molding. The internal tubings 18a, 18b are preferably independent of one another. This degree of freedom advantageously makes it possible to reduce the mechanical stresses in the collector 10, in particular during the temperature rise of the collector 10 due to the passage of an exhaust gas flow in one of the internal tubes 18a, 18b, since the expansion of a tubular 18a, 18b is not thwarted by the other internal tubing. The two internal pipes 18a, 18b have, at their outlet 20a, 20b, a section in the form of a half disc. Thus, the two internal tubes 18a, 18b are substantially in a circle at their outlet 20a, 20b.

  A coating 22 of thermal insulating material fills the space between the internal tubes 18a, 18b and the inner wall of the inlet ducts 14a, 14b. This coating 22 made of thermal insulating material is an integral part of the molding core of the outer structure 12. In this case, this coating 22 of thermal insulating material is made of fibrous material and more particularly rockwool, a material resistant to high temperatures and to molten iron. The rock wool may also be replaced by any material, preferably fibrous, which may form an integral part of the molding core of the outer structure 12, the fibrous material having to withstand especially the melting melt. Thus, advantageously, a sand core traditionally used during the manufacture of an exhaust manifold and in particular during the molding of the external structure of such an exhaust manifold, is no longer necessary. Advantageously, in the case of the invention, it is not necessary to remove this coating of thermal insulating material after the molding of the external structure 12.

  As illustrated in FIG. 1, the double-walled and two separate long-pipe manifolds 14a, 14b comprise two inlet flanges 24a, 24b, in line along the axis XX 'into which the inlet ends open out. 26a, 26b of the two internal tubes 18a, 18b disposed respectively in the inlet ducts 14a, 14b of the outer structure 12. Each inlet flange 24a, 24b has a central opening 28a, 28b and extends parallel to the plane interface so as to be sealed to the engine cylinder head, possibly with a seal between the bearing surfaces of the inlet flanges and the exhaust face of the cylinder head, so as to connect the internal manifolds 18a, 18b of the manifold 10 with the exhaust ducts of the corresponding cylinders (not shown).

  The collector 10 also comprises an outlet flange 30 extending, in this case, substantially perpendicular to the plane of FIG. 1, which is intended to be connected to the engine exhaust line (not shown) and to the center of the engine. which open the two internal tubes 18a, 18b.

  Substantially at the outlet flange 30, the internal tubes 18a, 18b are encircled by a sleeve 32 which separates the internal tubes 18a, 18b from the external structure 12. Preferably, this sleeve 32 is mounted with a clearance between the internal tubing 18a, 18b and the inner wall of the outlet duct 16, the expansion set allowing thermal fluctuations without stresses at the internal tubings 18a, 18b. This bushing 32 is held in position by a shoulder 34 formed by the inner wall of the outlet duct 16.

  Thus, advantageously, the internal tubings 18a, 18b of the external structure 12 are thermally insulated without generating mechanical stresses on the internal tubings 18a, 18b. In particular, the internal tubes 18a, 18b are allowed to expand independently of each other when one of them becomes heated due to the passage of a flow of hot exhaust gases.

  The sleeve 32 is made of steel and may or may not be of the same shade as the internal tubes 18a, 18b.

  Figures 2 and 3 respectively show an external structure and a set of four internal tubes capable of cooperating. In these figures, elements identical to those of Figure 1 or having the same function are indicated by the reference of the element of Figure 1 increased by 100.

  The outer structure 112 shown in Figure 2 has four inlet ducts 114a, 114b, 114c, 114d joining to form an outlet duct 116.

  The four inlet ducts 114a, 114b, 114c, 114d open on the side opposite their junction, at four inlet flanges 124a, 124b, 124c, 124d in line along the axis XX 'capable of allowing the watertight fastening. collector on the cylinder head of a four-cylinder engine in line. The outlet duct 116 opens at an outlet flange 130 adapted to allow the sealed attachment of the collector according to the invention to an exhaust line.

  FIG. 3 shows a set of four internal tubes 118a, 118b, 118c, 118d able to be mounted inside the external structure 112 shown in FIG. 2. As can be seen in FIG. 3, the internal tubes 118a, 118b, 118c, 118d have, near their outlet 120a, 120b, 120c, 120d a section substantially in the form of a quarter circle, so as to be encircled by a single cylindrical metal sleeve (not shown) separating them from the inside of the outlet duct 116 of the external structure 112. Thus, the internal tubes 118a, 118b, 118c, 118d, encircled by a metal bushing as described above with reference to FIG. the inner wall of the outlet duct 116 near the outlet of the outlet duct 116.

  As regards the manufacture of a collector according to the invention, among the moldable materials that can be used include: cast irons 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.

  The choice of materials for the realization of the internal pipes 18a, 18b, 118a, 118b, 118c, 118d, the sleeve 32 and the external structure 12, 112 is very important since it is to ensure the seal between the different components of the collector according to the invention, this seal to be provided by a natural hooping related to the withdrawal of the molded metal on the internal pipes.

  The manufacture of an exhaust manifold according to the invention can be achieved by the implementation of a method comprising at least the following operations: a) Fabrication of the various internal tubes 18a, 18b, 118a, 118b, 118c, 118d ; b) Covering each inner tubing 18a, 18b, 118a, 118b, 118c, 118d separately or all of the internal tubings by a coating 22 of thermal insulating material; c) Placing all the internal tubings 18a, 18b, 118a, 118b, 118c, 118d and the coating 22 of thermal insulating material; and d) pouring the outer structure 12, 112.

  Between operations a) and c), before or after operation b), the following operation e) can be carried out: e) placing a bushing 32 at the outlet of the internal tubes 18a, 18b, 118a, 118b, 118c, 118d.

  By performing this operation e) before operation d), advantageously protects the internal tubes 18a, 18b, 118a, 118b, 118c, 118d of the molten cast iron during molding of the external structure 12, 112.

  Preferably, internal tubings 18a, 18b, 118a, 118b, 118c, 118d are made longer than necessary so as to ensure correct positioning of the internal tubings in said mold and then the excess parts of the internal tubings are removed after casting or molding of the outer structure.

  More preferably, the thermal insulating material is a fibrous material. In fact, by using a thermal insulating fibrous material, the step of molding the insulating material is dispensed with.

  Such a manufacturing method is very advantageous compared to the manufacture of a mechanically welded double-walled collector since, since the external structure is molded, it is possible to eliminate the welds necessary for the manufacture of a mechanically welded double-walled collector. , the welds being, as said above, sources of reliability problems. Moreover, the possibility of having a molded structure greatly reduces the geometrical dispersions of the final piece. In particular, the position of the outlet flange relative to the inlet flange is substantially ensured, which is difficult to obtain with a mechanically welded double-walled collector. Furthermore, a method of manufacturing with molding of the external structure is also very advantageous concerning the cost of manufacture since the raw materials used and the foundry processes used are more economical than in the context of the manufacture of a collector. double welded wall.

  The manufacturing method of the collector according to the invention is also advantageous compared to the manufacturing method of a collector implementing a sand core for molding the external structure. Indeed, by eliminating the step of emptying the sand after the molding of the external structure, it leads to a significant time saving which results in a gain on the manufacturing cost.

  The invention is not limited to the single embodiment described here by way of illustrative and nonlimiting example and many embodiments are possible without departing from the scope of the invention.

  In particular, it goes without saying that the number of internal tubings can be different without departing from the scope of the invention.

  Furthermore, it is conceivable that the exhaust manifold according to the invention comprises several outlet ducts so as to evacuate the exhaust gas on one or more separate exhaust lines.

Claims (10)

  An exhaust manifold (10) of the double-wall type with long separate ducts for an internal combustion engine, characterized in that it comprises: a molded external structure (12, 112) provided with several inlet ducts ( 14a, 14b, 114a, 114b, 114c, 114d) joining together to form at least one outlet duct (16, 116), - an internal gas guiding pipe (18a, 18b, 118a, 118b, 118c, 118d) arranged within each of said inlet ducts (14a, 14b, 114a, 114b, 114c, 114d) leaving a space between said internal tubing (18a, 18b, 118a, 118b, 118c, 118d) and said inlet duct corresponding (14a, 14b, 114a, 114b, 114c, 114d), the external structure (12, 112) having inlet flanges (24a, 24b, 124a, 124b, 124c, 124d) into which said inlet ducts (14a, 14b, 114a, 114b, 114c, 114d) and said internal tubings (18a, 18b, 118a, 118b, 118c, 118d), and at least one outlet flange (30, 130) into which said at least one outlet duct (16, 116) and said internal ducts (18a, 18b, 114d) or outlet ducts (16, 116) being filled with a coating (22) of thermal insulating material forming an integral part of the molding core of the outer structure (12, 112).   2. Exhaust manifold (10) according to claim 1, characterized in that, in the vicinity of said at least one outlet flange (30, 130), said internal tubes (18a, 18b, 118a, 118b, 118c, 118d ) are encircled by a steel bushing (32), separating said inner tubes (18a, 18b, 118a, 118b, 118c, 118d) from said at least one outlet duct (16, 116).   3. exhaust manifold (10) according to claim 2, characterized in that said sleeve (32) made of steel is mounted, with expansion gap, between said internal tubes (18a, 18b, 118a, 118b, 118c, 118d). and said at least one outlet duct (16, 116).   4. Exhaust manifold according to one of claims 1 to 3, characterized in that said coating (22) of thermal insulating material is a fibrous material.   118a, 118b, 118c, 118d), said space between said internal tubings (18a, 18b, 118a, 118b, 118c, 118d) and said inlet ducts (14a, 14b, 114a, 114b, 114c, 5. exhaust manifold according to any one of the preceding claims, characterized in that said thermal insulating material comprises rock wool.   6. Exhaust manifold according to any one of the preceding claims, characterized in that, at their end facing said inlet flanges (24a, 24b, 124a, 124b, 124c, 124d) said internal tubes (18a, 18b 118a, 118b, 118c, 118d) are disengaged from said coating (22) of thermal insulating material.   7. Exhaust manifold according to any one of the preceding claims, characterized in that at their end facing said inlet flanges (24a, 24b, 124a, 124b, 124c, 124d) said inner tubes (18a, 18b , 118a, 118b, 118c, 118d) are mounted in the outer structure (12, 112) with a set of expansion.   8 A method of manufacturing an exhaust manifold (10) according to any one of the preceding claims, characterized in that it comprises at least the following operations: a) Manufacturing the various internal tubes (18a, 18b, 118a, 118b, 118c, 118d); b) Covering each inner tubing (18a, 18b, 118a, 118b, 118c, 118d) separately or all of the inner tubings (18a, 18b, 118a, 118b, 118c, 118d) by a coating (22) of material thermal insulator; c) Placing all the internal tubes (18a, 18b, 118a, 118b, 118c, 118d) and the coating (22) of thermal insulating material; and d) casting or molding the outer structure (12, 112).   9. The method of claim 8, taken in combination with one of claims 2 and 3, characterized in that it further comprises, between operations a) and c), before or after operation b), e) following: e) placing a bushing (32) at the outlet of the internal tubes (18a, 18b, 118a, 118b, 118c, 118d.   10. Method according to one of claims 8 and 9, characterized in that it carries internal tubings (18a, 18b, 118a, 118b, 118c, 118d) longer than necessary so as to ensure a correct positioning of said internal tubes. (18a, 18b, 118a, 118b, 118c, 118d) in said mold and in that the excess portions of the internal tubings (18a, 18b, 118a, 118b, 118c, 118d) are removed after the casting of said external structure (12, 112).