Patent Publication Number: US-2019186324-A1

Title: Heat recovery device and corresponding manufacturing process

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. non-provisional application claiming the benefit of French Application No. 1762294, filed on Dec. 15, 2017, which is incorporated herein by herein in its entirety. 
     FIELD OF INVENTION 
     The invention generally relates to heat recovery devices for exhaust lines. 
     BACKGROUND OF THE INVENTION 
     Motor vehicle exhaust lines may include heat exchangers of the type shown in  FIG. 1 . Such a heat exchanger  1  comprises a plurality of exhaust gas circulation tubes  3 . These tubes  3  are held at each of their longitudinal ends by a grate  5 . A casing  7  is placed around the tubes  3  and grates  5 . The tubes  3 , the grates  5 , and the casing  7  are attached to one another by brazing in a furnace. 
     Each grate  5  includes an upright edge  9  oriented toward an outside of the heat exchanger  1 , to be attached on a body  11 , shown in  FIG. 2 . The body  11  is, for example, integrated into a three-way valve making it possible to orient the exhaust gases selectively either toward the heat exchanger  1  or toward a bypass pipe of the heat exchanger  1 . An end rim  13  of the upright edge  9  must be far enough away from the junction between the grate  5  and the casing  7  so as not to cause the braze securing the grate  5  to the casing  7  to melt during the welding of the grate  5  on the body  11 . 
     The grate  5  has a generally rectangular shape. It may be formed from a flat metal sheet, the sides of which are folded down to give it a basin shape, and thus to create the upright edge  9 . The metal sheet is next pierced to create orifices for receiving the tubes  3 . 
     During the shaping of the flat metal sheet, the material is compressed at each corner of the upright edge  9 . The surface condition inside the four corners is not good. Folds can be seen both inside and outside the basin. 
     Thus, the shaping of the grate  5  does not make it possible to have a good surface condition, or good dimensional allowances, in each corner of the upright edge  9 . 
     Furthermore, it is difficult to obtain good flatness of each of the sides of the upright edge  9 . This is due to the resilient return of the material in the four corners. 
     Furthermore, as visible in  FIG. 2 , the exchanger  1  can be attached to a barrel stretcher  15  arranged in the body  11 . The upright edge  9  is inserted inside the barrel stretcher  15 . 
     Although the barrel stretching is obtained by an elongation of the material and not by compression, the edges of the barrel stretcher  15  are absolutely not planar, due to the resilient return of the material during the shaping. The edges of the barrel stretcher  15  are not perpendicular to the plane of the opening delimited in the body  11 , the undercut angle being approximately 2°. 
     Thus, the play between the upright edge  9  of the grate  5  and the barrel stretcher  15  is not constant, and may be greater than 0.5 mm on average. 
     It is possible to consider butt welding the upright edge  9  and the barrel stretcher  15 , in the configuration shown in  FIG. 2 . 
     In the exhaust field, the welding method traditionally used is MAG (Metal Active Gas). With such a welding method, the significant play between the upright edge  9  and the barrel stretcher  15  may generate defects, or even holes. 
     For lap welding, it would be necessary to have the upright edge  9  and the barrel stretcher  15  go past one another. Yet the length of the upright edge  9  is limited by the fact that the compression of the material in the corners becomes impossible past a certain limit. 
     Likewise, the barrel stretcher  15  has a maximum length, related to the acceptable maximum elongation of the material. 
     Furthermore, the MAG method has certain known flaws, the most significant of which is deforming the parts to be welded, because these parts are heated to a high temperature, and locally. 
     This flaw is particularly critical when the heat exchanger  1  must be rigidly attached to a valve body, which must have a good final geometry in order for the axis of the flap to be able to rotate without interference with the valve body, and for the valve to have a good sealing level. 
     In this context, the invention aims to propose a heat recovery device that does not have the above flaws. 
     SUMMARY OF THE INVENTION 
     The invention relates to a heat recovery device for an exhaust line, the device comprising a body inwardly delimiting an exhaust gas circulation passage, and a heat exchanger, the heat exchanger comprising: 
     a casing having a proximal edge delimiting a proximal opening; 
     a plurality of exhaust gas circulation tubes, extending inside the casing; 
     at least one grate arranged in the proximal opening, the at least one grate comprising a wall in which orifices are arranged, each exhaust gas circulation tube having a proximal end engaged in one of the orifices and attached to the at least one grate, the at least one grate further having an upright edge extending around the wall and protruding from the wall toward an inside of the heat exchanger, the upright edge being rigidly attached to the casing; 
     the wall of the at least one grate having, around the orifices, a planar surface turned toward the body; 
     the body having a body opening delimited by a flat edge pressed against the planar surface; and 
     the planar surface and the flat edge being rigidly attached to one another to be tight with respect to exhaust gases. 
     Thus, in the invention, the at least one grate is turned in a direction opposite  FIG. 1 . This makes it possible to make the connection between the body and the grate at the planar surface of the grate surrounding the receiving orifices of the tubes. It is therefore no longer necessary to perform barrel stretching around the opening of the body, the connection between the body and the grate being done at two planar surfaces that are parallel to one another. 
     This advantageously makes it possible to secure the at least one grate and the body through either a brazing method or a laser welding method. 
     These methods are advantageous, since they do not require considerable heating of the parts, and therefore minimize the risk of deformation of the body. 
     Obtaining good flatness of the planar surface of the at least one grate and the flat edge of the body is easier than monitoring the geometry of the barrel stretching or the upright edge on the device of  FIGS. 1 and 2 . 
     Furthermore, the height of the upright edge is less significant than in  FIGS. 1 and 2 , since it is not necessary to extend the latter to the free edge of the barrel stretcher. It is only necessary to provide the junction with the casing of the heat exchanger. The manufacture of the at least one grate is easier, and the deformations are less pronounced. 
     The heat recovery device may also have one or more of the features below, considered individually or according to all technically possible combinations: 
     the planar surface and the flat edge are rigidly attached to one another by laser welding or by brazing; 
     the upright edge of the at least one grate is rigidly attached to the proximal edge of the casing, the wall of the at least one grate being offset toward an outside of the casing; 
     the planar surface has a closed contour and has a width of at least two millimeters; 
     the casing includes a central tubular part having a first straight section, the proximal opening having a second section greater than the first straight section; 
     the proximal edge of the casing is connected to the central tubular part by a tubular segment that flares from the central tubular part, the tubular segment delimiting a heat transfer fluid circulation channel along the at least one grate; 
     the casing has a heat transfer fluid inlet and a heat transfer fluid outlet, the heat transfer fluid inlet being arranged in the central tubular part, the central tubular part having a zone protruding toward the outside of the casing extending from the heat transfer fluid inlet to the heat transfer fluid circulation channel along the at least one grate; 
     the exhaust gas circulation tubes have protuberances forming spacers maintaining a determined spacing between the exhaust gas circulation tubes, and between the exhaust gas circulation tubes and the casing, the protuberances in contact with the casing all being located outside the heat transfer fluid circulation channel along the grate; 
     the planar surface extends in a first plane, the orifices being surrounded by a ridge adjacent to the planar surface, the ridge extending in a second plane parallel to the first plane and offset toward the inside of the heat exchanger relative to the first plane. 
     According to a second aspect, the invention relates to a method for manufacturing a heat recovery device having the above features, 
     assembling the casing, the exhaust gas circulation tubes and the at least one grate to one another by brazing; and 
     attaching the planar surface of the at least one grate and the flat edge of the body to one another by laser welding or by brazing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the invention will emerge from the detailed description thereof provided below, for information and non-limitingly, in which: 
         FIG. 1  is a cross-sectional view of a heat exchanger not according to the invention; 
         FIG. 2  is a sectional view of one end of the heat exchanger of  FIG. 1 , attached on a body; 
         FIG. 3  is an exploded view of heat exchanger of a heat recovery device according to the invention; 
         FIG. 4  is a longitudinal sectional view of the heat exchanger of  FIG. 3 , in the assembled state; 
         FIG. 5  is a sectional view of one end of the heat exchanger of  FIGS. 3 and 4 , attached on a body; 
         FIG. 6  is a perspective view of the heat exchanger of  FIGS. 3 to 5 ; 
         FIG. 7  is a bottom view of the heat exchanger, for an alternative embodiment; 
         FIG. 8  is an enlarged sectional view of part of one of the grates of the heat exchanger of  FIGS. 3 and 4 ; and 
         FIG. 9  is a perspective view of the grate of  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION 
     The heat recovery device  17  is provided to be integrated into an exhaust line, typically an exhaust line of a vehicle equipped with a heat engine. The vehicle is, for example, a motor vehicle, typically a car or truck. 
     The heat recovery device  17  is provided to recover part of the heat energy from the exhaust gases circulating in the exhaust line. The heat energy thus recovered is used on board the vehicle, for example to accelerate the temperature increase of the heat engine, or to heat the passenger cab. 
     The heat recovery device  17  shown in  FIGS. 3 to 5  comprises a body  19  ( FIG. 5 ) inwardly delimiting an exhaust gas circulation passage  21 , and a heat exchanger  23 . 
     The body  19  has an opening  25 , through which the circulation passage  21  communicates with the heat exchanger  23 . 
     The body  19  is, for example, a valve body. In this case, the valve is typically a three-way valve, the body  19  having at least one exhaust gas inlet and two outlets, all communicating fluidly with the circulation passage  21 . The inlet is in fluid communication with a collector capturing the exhaust gases at the outlet of the combustion chambers of the heat engine. One of the outlets constitutes the opening  25  and communicates with the exhaust gas circulation side of the heat exchanger  23 . The other outlet emerges in a bypass pipe of the heat exchanger. In  FIG. 5 , only one opening  25  has been shown. 
     Alternatively, the body  19  is an exhaust gas circulation pipe, the heat exchanger being mounted in a bypass on said pipe. 
     As illustrated in  FIGS. 3 to 5 , the heat exchanger  23  comprises a casing  27 , and a plurality of exhaust gas circulation tubes  29 , extending inside the casing  27 . 
     The tubes  29  communicate fluidly with the circulation passage  21  through the opening  25 . 
     The casing  27  has a proximal edge  31 , delimiting a proximal opening  33 . 
     It also includes a distal edge  35 , delimiting a distal opening  37 . The proximal edge  31  and the distal edge  35  have closed contours. 
     The heat exchanger  23  also includes at least one grate  39 , arranged in the proximal opening  33 . The grate  39  comprises a wall  41  in which orifices  43  are arranged. 
     Each tube  29  has a proximal end  45 , arranged in one of the orifices  43  and attached to the grate  39 . 
     Advantageously, the heat exchanger  23  comprises another grate  47  arranged in the distal opening  37 . The other grate  47  comprises a wall  49  in which orifices  51  are arranged. Each tube  29  has a distal end  53  engaged in one of the orifices  51  and attached to the other grate  47 . 
     Typically, the grate  39  and the other grate  47  are identical in all points. Only the grate  39  will therefore be described below in detail. 
     Preferably, the tubes  29  are rectilinear, and extend longitudinally from the proximal end  45  to the distal end  53 . 
     For example, the tubes  29  have, in a transverse plane perpendicular to the longitudinal direction, a substantially rectangular section, constant over the entire longitudinal length of the tube  29 . The section is elongated along a transverse direction T. The longitudinal L and transverse T directions are shown in  FIG. 3 . 
     Each tube  29  therefore has two large faces  55 ,  57 , opposite one another, and connected to one another by sheared edges  59 . The large faces  55 ,  57  extend substantially in planes containing the longitudinal L and transverse T directions. These planes are perpendicular to an elevation direction E, embodied in  FIG. 3 . 
     Advantageously, the tubes  29  are all stacked along the elevation direction. In other words, the heat exchanger  23  in a transverse plane comprises no more than a single tube. 
     Each tube  29  therefore extends practically over the entire transverse width of the heat exchanger  23 . The tubes  29  are stacked such that the large base  55  of a given tube is placed across from the large base  57  of the tube immediately below it in the stack along the elevation direction. 
     Fins  62  are placed inside each tube  29  to promote heat exchanges on the gas side. The fins  62  are, for example, made in the form of a metal sheet folded in an accordion and inserted inside the tube  29 . 
     The orifices  43  and  51  of the grates  39  and  47  have a shape conjugated with that of the tubes  29 . They therefore have a transversely elongated shape and extend over practically the entire width of the grate. They are arranged in a single column. 
     The grate  39  comprises an upright edge  60 , extending around the wall  41  and protruding from the wall  41  toward the inside of the heat exchanger  23 . 
     In the illustrated example, the wall  41  is substantially rectangular, with rounded corners. As a result, the upright edge  60  includes two segments  61  that are substantially parallel to one another and extend along the transverse direction T, and two segments  63  that are substantially parallel to one another and extend along the elevation direction E. Preferably, the two segments  61  are parallel to one another and extend along the transverse direction T. Preferably, the two segments  63  are parallel to one another and extend along the elevation direction E. The segments  61  and  63  are connected to one another by curved portions. 
     The upright edge  60  protrudes along the longitudinal direction L. As shown in  FIG. 4 , the upright edge  60  is engaged in said the proximal edge  31  of the casing  27 , the proximal edge  31  being pressed against an outer surface of the upright edge  60 . The upright edge  60  is rigidly attached to the casing  27 . More specifically, the proximal edge  31  is brazed on the upright edge  60 . 
     The wall  41  of the grate  39  is offset toward the outside of the casing  27 . The wall  41  is offset along the longitudinal direction L. This means that the wall  41  is not located inside the casing  27 , but is located longitudinally past the proximal end  31  of the casing  27 . 
     The wall  41  of the grate  39  has, around the orifices  43 , a planar surface  65  turned toward the body  19 . 
     Typically, the planar surface  65  extends in a determined plane. This plane is perpendicular to the longitudinal direction L and therefore contains the transverse direction T and the elevation direction E. 
     The planar surface  65  extends all around the orifices  43 . The planar surface  65  therefore has a closed contour. 
     It has a width of at least 2 mm, for example of between 2 and 5 mm. This width is taken along a direction perpendicular to a junction line  67  between the upright edge  60  and the wall  41 . In other words, this width is taken along the elevation direction E along the segment  61  of the upright edge  60 , and along the transverse direction T along the segment  63  of the upright edge  60 . 
     The planar surface  65  extends, in the illustrated example, up to the junction line  67  between the upright edge  60  and the wall  41 , i.e., up to the outer edge of the wall  41 . 
     The opening  25  is cut out in a wall of the body  19 . 
     Typically, it is cut out in a substantially planar zone  68  of the wall, preferably with a flatness of less than 0.3. This planar zone  68  delimits, on one side, the inside of the circulation passage  21 , and is therefore in direct contact with the exhaust gases. On the opposite side, it is in contact with the grate  39  of the heat exchanger. 
     The opening  25  of the body  19  is delimited by a flat edge  69 , pressed against the planar surface  65 . 
     The flat edge  69  is therefore in contact on one side with the planar surface  65 , and on the opposite side of the planar surface  65 , with the exhaust gases circulating in the body  19 . 
     The planar surface  65  and the flat edge  69  are rigidly attached to one another to be tight with respect to the exhaust gases. 
     The planar surface  65  and the flat edge  69  are directly attached to one another. 
     The planar surface  65  and the flat edge  69  are rigidly attached to one another by laser welding or by brazing. 
     The planar zone  68  does not bear any relief around the flat edge  69 , which makes it possible to adjust the position of the grate  39  relative to the body  19 . 
     It should be noted that the other grate  47  is also mounted on a planar zone, such that it is possible to adjust the positions of both ends of the heat exchanger relative to one another. 
     The flat edge  69  has, toward the heat exchanger  23 , a planar outer surface  71 , pressed against the planar surface  65 . 
     This planar outer surface  71  extends in a plane, said plane being perpendicular to the longitudinal direction L in the illustrated example. 
     The edge  69  has a closed contour and extends all the way around the opening  25 . 
     The opening  25  has a size and shape such that all of the orifices  43  are located in line with said opening  25 . The proximal ends  45  of the tubes  29  protrude past the grate  39 , and penetrate slightly inside the opening  25 , as illustrated in  FIG. 5 . 
     The heat exchanger  23  also includes a reinforcing grate  73 , arranged to reinforce the connection between the tubes  29  and the grate  39 . It advantageously includes another reinforcing grate  75 , arranged to reinforce the connection between the tubes  29  and the other grate  47 . The grate  73  and the grate  75  are identical, only the grate  73  therefore being described below. 
     The reinforcing grate  73  is a plate in which apertures  77  have been arranged. The apertures  77  are delimited by necks  79  ( FIG. 5 ) and are each passed through by the proximal end  45  of one of the tubes  29 . The apertures  77  are each placed across from one of the orifices  43 . The necks  79  are brazed on the tubes  29 . The peripheral edge  81  of the reinforcing plate, and the fields  83  located between the apertures  77 , are brazed on the inner surface of the wall  41 . 
     In the illustrated example, the proximal edge  31  and the distal edge  35  of the casing  27  are located at the two opposite longitudinal ends thereof. 
     The casing  27  is made in two half-shells  85 ,  87 . The half-shells  85 ,  87  are secured to one another by brazing, along two longitudinal lines  89  ( FIG. 6 ). 
     Each half-shell  85 ,  87  has a U-shaped section in a plane perpendicular to the longitudinal direction L. 
     The casing  27  includes a central tubular part  91  having a first straight section, the proximal opening  33  having a second section greater than the first section ( FIG. 4 ). Likewise, the distal opening  37  has a section greater than the first section, and typically equal to the second section. 
     To that end, the proximal edge  31  of the casing  27  is connected to the central tubular part  91  by a tubular segment  93  that flares from the central tubular part  91 . 
     Likewise, the distal edge  35  of the casing  27  is connected to the central tubular part  91  by another tubular segment  95  that flares from the central tubular part  91 . 
     The tubular segment  93  delimits a heat transfer fluid circulation channel  97  along the grate  39 . Likewise, the tubular segment  95  delimits a heat transfer fluid circulation channel  98  in contact with the other grate  47 . 
     The passage section offered to the heat transfer fluid by the circulation channel  97 , and also by the circulation channel  98 , is significantly greater than in the heat exchanger shown in  FIG. 1 . 
     This results from several constructive arrangements of the heat exchanger. 
     First of all, the planar surface  65  of the wall  41  is significantly wider in the invention than in the heat exchanger of  FIG. 1 . Indeed, this planar surface  65  is deliberately made wider in the invention, to allow good quality tight attachment of the flat edge  69  on the planar surface  65 . 
     Furthermore, as previously stressed, in the invention, the wall  41  is offset toward the outside of the casing  27 . In the heat exchanger of  FIG. 1 , the wall in which the receiving orifices of the tubes are arranged is placed inside the casing  7 . 
     This large passage section of the circulation channel  97  is particularly advantageous, since it is thus possible to increase the heat transfer fluid flow rate in contact with the grate  39 . The grate  39  is typically located at the exhaust gas inlet inside the heat exchanger. Yet the heat exchangers used in exhaust lines must never come to a boil. The most critical zone with respect to boiling is always located on the exhaust gas inlet side, i.e., in the zone where the exhaust gases are hottest. In case of boiling, the heat transfer fluid turns to vapor, such that the heat exchanges at the inlet of the heat exchanger are gas-gas locally. As a result, the skin temperature of the exchanger increases quickly, and may approach the temperature of the exhaust gases (for example, around 850° C.). This risks locally creating a thermal shock and temperature gradients causing breaks, and therefore leaks, at the brazes securing the various components of the heat exchanger to one another. 
     It is therefore critical for a heat exchanger of this type for the heat transfer fluid flow rate in the grate  39  to be high enough to prevent any risk of boiling. 
     The casing  27  has a heat transfer fluid inlet  99  and a heat transfer fluid outlet  101  ( FIGS. 3 and 6 ). 
     In the illustrated example, the heat transfer fluid inlet  99  and outlet  101  are arranged in the half-shell  87 . The heat transfer fluid inlet  99  and outlet  101  are arranged side by side, and offset longitudinally relative to one another. The inlet  99  is located on the side of the grate  39 , and the outlet  101  on the side of the grate  47 . In other words, the heat transfer fluid inlet  99  is located toward the exhaust gas inlet and the heat transfer fluid outlet  101  toward the exhaust gas outlet. 
     The heat transfer fluid inlet  99  is located in the central tubular part  91  of the casing  27 . Advantageously, and as illustrated in  FIG. 7 , the central tubular part  91  has a zone  103  protruding toward the outside of the casing  27 , extending from the heat transfer fluid inlet  99  to the heat transfer fluid circulation channel  97 , along the grate  39 . 
     The zone  103  is not shown in  FIGS. 3 to 5 . 
     More specifically, the casing  27  has two large faces  105  and  107 , which are substantially perpendicular to the elevation direction E, and two side faces  109 , which are substantially perpendicular to the transverse direction T, and connecting the faces  105  and  107  to one another. The heat transfer fluid inlet  99 , and typically the heat transfer fluid outlet  101 , are arranged in one of the side faces  109 . The protruding zone  103  is advantageously arranged on the large face  107 . It has a generally triangular shape, as shown in  FIG. 7 . It extends transversely from the heat transfer fluid inlet  99  to the side face  109  opposite the heat transfer fluid inlet  99 . Its width, taken along the longitudinal direction, decreases from the heat transfer fluid inlet  99  toward the side face  109  opposite the heat transfer fluid inlet  99 . 
     Advantageously, the protruding zone  103  protrudes relative to a central zone  111  of the central tubular part  91  over a height substantially equal to that of the proximal end  31 . 
     The protruding zone  103  makes it possible to collect the heat transfer fluid at the heat transfer fluid inlet  99 , and to steer it preferentially toward the circulation channel  97 . This promotes the cooling at the inlet of the heat exchanger and limits the risk of boiling. 
     Advantageously, the casing  27  also includes another protruding zone  112 , extending from the heat transfer fluid outlet  101  to the heat transfer fluid circulation channel  98  along the other grate  47  ( FIG. 7 ). 
     The protruding zone  112  is symmetrical with the protruding zone  103  relative to the median plane of the heat exchanger perpendicular to the longitudinal direction L. 
     The tubes  29  have protuberances  113  forming spacers maintaining a determined spacing between the tubes  29 , and between the tubes  29  and the casing  27 . These protuberances  113  are distributed on the large faces  55  and  57  of the tubes. 
     In the illustrated example, each of the large faces  55 ,  57  has around ten protuberances  113 . 
     The protuberances  113  protrude toward the outside of the tubes  29 . They are obtained by deformation of the metal making up the tube  29 . 
     The protuberances  113  in contact with the casing  27  are all located outside the heat transfer fluid circulation channel  97  along the grate  39 , and typically also outside the heat transfer fluid circulation channel  98  along the other grate  47 . 
     This is favorable to the mechanical strength between the casing  27  and the protuberances  113 . 
     Preferably, these protuberances are also located outside the protruding zone  103  and outside the protruding zone  112 . 
     Typically, the protuberances  113  formed on the large faces  55  of a tube  29  are located across from the protuberances  113  formed on the large faces  57  of said same tube  29 . “Across from” means opposite one another along the elevation direction E. Likewise, the protuberances  113  formed on a given tube  29  are located in the extension of the protuberances  113  of the other tubes  29  along the elevation direction E, as illustrated in  FIG. 4 . In other words, all of the tubes  29  have protuberances  113  having the same arrangement on their two opposite large faces  55 ,  57 , such that said protuberances  113  form stacks in a column, along the elevation direction E. This is favorable to increasing the rigidity of the heat exchanger  23 . 
     According to another advantageous aspect of the invention, the planar surface  65  of the grate  39  extends in a first plane P 1 , the orifices  43  being surrounded by a ridge  115  adjacent to the planar surface  65 , the ridge  115  extending in a second plane P 2  parallel to the first plane P 1  and offset toward the inside of the heat exchanger  23  relative to the first plane P 1 . This is illustrated in  FIG. 8 . 
     The ridge  115  extends over the entire perimeter of the orifices  43 . It has a closed contour, and is inwardly adjacent to the planar surface  65 . It is separated from the planar surface  65  by a step. 
     Thus, during the brazing of the heat exchanger  23 , the brazing material cannot spread over the planar surface  65 . It is retained by the step separating the ridge  115  from the planar surface  65 . 
     According to another aspect, the invention relates to the process for manufacturing the heat recovery device  17  described above. 
     This manufacturing process comprises the following steps: 
     assembly by brazing the casing  27 , tubes  29  and grate  39  to one another; 
     attaching the planar surface  65  of the grate  39  and the flat edge  69  of the body  19  to one another by laser welding or by brazing. 
     Typically, in the assembly step, the other grate  47  is assembled by brazing to the casing  27  and the tubes  29 . 
     Furthermore, the reinforcing grates  73 ,  75  are advantageously assembled by brazing to the tubes  29  and the grates  39 ,  47 , in the same step. 
     The assembly step also makes it possible to secure the half-shells  85 ,  87  of the casing  27  to one another. 
     As described above, the casing  27  is assembled to the grate  39  by brazing of the proximal edge  31  on the upright edge  60 . 
     The tubes  29  are assembled to one another by brazing, said brazing preferably being done at the protuberances  113 . 
     The tubes  29  are assembled to the casing  27  by brazing of the protuberances  113  on the casing  27 , and more specifically on the central tubular part  91  of the casing  27 . 
     The brazing step is advantageously done in a furnace. 
     When the attachment of the planar surface  65  on the flat edge  69  is done by laser welding, this welding is done by transparency, through the flat edge  69 . The weld line has a closed contour, and extends over the entire perimeter of the opening  25 . 
     When the attachment is done by brazing, brazing paste is deposited between the flat edge  69  and the planar surface  65 . The brazing paste is melted, for example, by placing the body  19  and the heat exchanger  23  in a furnace. In this case, the brazing of the planar surface  65  and the flat edge  69  can be done at the same time as the assembly by brazing of the different elements of the heat exchanger to one another. 
     The heat recovery device  17 , and the corresponding manufacturing process, can assume multiple variants. 
     The grate  47  arranged in the distal opening  37  of the casing  27  could be of a different type from that arranged in the proximal opening  33 . 
     The tubes  29  do not necessarily have the shape described above. They could a circular section, an oval section, or any other appropriate section. These tubes are not necessarily rectilinear, but alternatively are curved. In this case, the distal opening  37  of the casing  27  is not necessarily placed longitudinally across from the proximal opening  33 . 
     The heat transfer fluid is typically a liquid. Alternatively, it is another type of fluid. 
     The heat exchanger  23  is not necessarily symmetrical relative to a median transverse plane of the heat exchanger. It may not include a circulation channel  98  of the heat transfer fluid in contact with the other grate  47  and/or not include a protruding zone  112 . 
     The wall  41  of the grate  39  may have all types of shapes. It is not necessarily rectangular. Alternatively, the wall  41  is circular, or elliptical, or has any other appropriate shape. 
     In this case, the opening  25  arranged in the body  19  also does not have a rectangular shape. It typically has a shape corresponding to the shape of the grate  39 , and more particularly to the shape of the wall  41 . 
     To attach the grate  39  to the casing  27 , the upright edge  60  is not necessarily engaged inside the proximal edge  31  of the casing  27 . Alternatively, it is the proximal edge  31  of the casing  27  that is engaged in the upright edge  60  of the grate  39 . 
     The casing  27  is not necessarily made up of two half-shells  85 ,  87  assembled to one another. It could be obtained by rolling a metal sheet around the longitudinal axis, or by deforming a tube segment. 
     The tubes  29  may be arranged in all types of different ways inside the heat exchanger  23 . In particular, it is possible to place several tubes  29  next to one another transversely and not just one as described above. 
     The planar surface  65  does not necessarily extend in a single plane. It may include several planar zones, arranged in several planes parallel to one another or tilted relative to one another. In these cases, the flat edge  69  has substantially the same shape as the planar surface  65 . In any case, the flat edge  69  and the planar surface  65  are in contact with one another over a zone with a closed contour surrounding the opening  25  and surrounding all of the orifices  43 ,  51 . This zone is wide enough to allow the attachment of the planar surface  65  and the flat edge  69  to one another, preferably by laser welding or by brazing. 
     Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this disclosure. For that reason, the following claims should be studied to determine the true scope and content of this disclosure.