Double-walled exhaust manifold

Abstract

The invention relates to a double-walled exhaust manifold ( 10 ) for a motor vehicle, said exhaust manifold comprising at least one inner element ( 12 ) provided with sliding tubes ( 16, 18 ) which fit into each other, and an outer element ( 14 ) which is moulded from a single piece around the inner element ( 12 ) with which it determines an inner insulation cavity ( 20 ). The inventive exhaust manifold is characterised in that the inner element comprises at least one first straight upstream tube ( 22 ), a first end ( 24 ) of said tube being arranged in the extension of an exhaust line of an associated heat engine cylinder head and a second end ( 26 ) fitting together, in a sliding manners with an intermediate part ( 28 ) of at least one downstream tube ( 16, 18 ) having an axis (B) intersecting the axis (A) of the first tube ( 22 ).

1 - 13 . (canceled) 
   
   
       14 . A double-walled exhaust manifold for a motor vehicle, comprising:
 at least one internal manifold element and one external manifold element,   wherein the internal manifold element includes at least two coaxial tubes nested slidingly one inside the other, and the external manifold element is cast in one piece around the internal manifold element, with which the external manifold element defines an internal insulating cavity disposed between the internal manifold element and the external manifold element, and   wherein the internal manifold element includes at least one straight first upstream tube, a first end of which is disposed in an extension of an exhaust conduit of a cylinder head of an associated heat engine, and a second end of which is nested slidingly with an intermediate part of at least one downstream tube whose axis intersects the axis of the first upstream tube, thereby permitting expansion of the internal manifold element during a rise in temperature of the manifold.   
   
   
       15 . An exhaust manifold according to  claim 14 , comprising at least one elbowed second upstream tube, a first end of which is disposed in an extension of an exhaust conduit of the cylinder head and a second end of which, with its axis intersecting the axis of the first end, is nested slidingly with the end of a downstream tube. 
   
   
       16 . An exhaust manifold according to  claim 14 , comprising at least two downstream tubes, one end of one downstream tube being nested slidingly with the end of the other downstream tube. 
   
   
       17 . An exhaust manifold according to  claim 14 , wherein the external manifold element includes a bore that communicates with the internal insulating cavity to permit evacuation of a sand core used to form the insulating cavity during casting of the external manifold element. 
   
   
       18 . An exhaust manifold according to  claim 14 , wherein the tubes of the internal manifold element are made of steel. 
   
   
       19 . An exhaust manifold according to  claim 14 , wherein the external manifold element is cast to confine at least one first end of an upstream tube and one end of a downstream tube. 
   
   
       20 . An exhaust manifold according to  claim 15  wherein the end of the straight first upstream tube and the first end of the elbowed second upstream tube extend to the first face of the external manifold element. 
   
   
       21 . An exhaust manifold according to  claim 20 , wherein one end of a downstream tube extends to a second face of the external manifold element. 
   
   
       22 . An exhaust manifold according to  claim 21 , further comprising means for preventing axial displacement of the ends of the upstream tubes and downstream tube that extend to the faces of the external manifold element. 
   
   
       23 . A method for manufacturing an exhaust manifold according to  claim 14 , comprising:
 a first step of manufacture of the tubes of the internal manifold element,   a second step of assembly of the tubes of the internal manifold element with one another,   a third step, during which the tubes of the internal manifold element are placed in a machine making it possible to form around the tubes, a sand core intended to permit casting of the insulating cavity,   a fourth step of casting of the sand core,   a fifth step, during which the tubes of the internal manifold element and the sand core are placed in a mold containing an imprint of the external manifold element,   a sixth step of casting of the external manifold element,   a seventh step of removal of the external manifold element from the mold,   an eighth step of removal of the sand core by abrasive blasting,   a ninth step of machining of the manifold, and   a tenth step of mounting of a sealing plug in the bore of the external manifold element.   
   
   
       24 . A method for manufacturing an exhaust manifold according to  claim 14 , comprising:
 a first step of manufacture of the tubes of the internal manifold element,   a second step of assembly of the tubes of the internal manifold element with one another,   a third step, during which the tubes of the internal manifold element are placed in a machine making it possible to form, around the tubes, a sand core intended to permit casting of the insulating cavity,   a fourth step of casting of the said sand core,   a fifth step, during which the tubes of the internal manifold element and the sand core are placed in a mold containing an imprint of the external manifold element,   a sixth step of casting of the external manifold element,   a seventh step of removal of the external manifold element from the mold,   an eighth step of removal of the sand core by abrasive blasting,   a ninth step of machining of the manifold and of the ends of the tubes that protrude beyond the faces of the external element, and   a tenth step of mounting of a sealing plug in the bore of the external manifold element.   
   
   
       25 . An internal combustion engine provided with a cylinder head and an exhaust manifold according to  claim 20 , wherein the ends which extend to the first face of the external element are in contact with the ends of the exhaust conduits of the cylinder head. 
   
   
       26 . An internal combustion engine according to  claim 25 , wherein the end which extends to the second face of the external element is in contact with one end of the exhaust pipe of the engine.