Exhaust gas heating device with metallic foam heating element

Abstract

Exhaust gas heating device with metallic foam heating element. Exhaust gas heating device (1) for an exhaust line of an internal combustion engine, comprising: - a housing (2) extending along an axis, - a heating element (4), in the form of a metallic foam disc having a thickness (Ee), housed in the housing (2) and occupying the entire cross-section of the housing (2), comprising substantially flat slots (12) in a plane parallel to the axis, substantially parallel to each other, passing through the thickness (Ee), and extending over a length strictly less than the width of the heating element (4), a slot (12) having a first end (14) opening at the periphery of the heating element (4) and a second end (16), alternating a first end (14) on one side and a first end (14) on the other side, from one slot (12) to the other.the heating element (4) comprising a densified material at the second ends (16). Abbreviated figure: Figure 2,

Description

Title of the invention: Exhaust gas heating device with metal foam heating element Technical field

[0001] The present invention relates to an exhaust gas heating device, intended to equip an exhaust line of an internal combustion engine, in particular an internal combustion engine of a vehicle. Prior art

[0002] It is known in the prior art to produce a device for catalytic purification of exhaust gases, in order to reduce polluting particles and in particular nitrogen oxides NOx, unburned hydrocarbons HC and carbon monoxide CO. It should be noted that the efficiency of this catalytic purification is optimal when the chemical oxidation-reduction reactions, namely reduction of NOx and oxidation of HC and CO, take place at high temperature. However, during a cold start, the exhaust gases are cold, resulting in less efficiency of the oxidation-reduction reactions, risking increasing pollutant emissions. Also, one solution consists of equipping the exhaust line with an exhaust gas heating device, upstream of the catalytic purification device.

[0003] It is also known to produce such a heating device by means of a metal foam, traversed by an electric current, so as to heat the foam by Joule effect. The exhaust gases circulate through a slice of heated metal foam and are thus heated.

[0004] According to a known embodiment, the metal foam is cut by substantially flat, parallel and alternating slits, so as to form an electrical path comprising a succession of lace turns, in order to be as long as possible and cover the entire surface so as to heat the latter uniformly.

[0005] The disadvantage of such an embodiment is that an electrical hot spot is created inside each hairpin bend, at the turning point. Such a hot spot is detrimental in that it creates a thermal hot spot, whereas thermal uniformity is sought over the entire passage surface of the heating device. Such a hot spot is further detrimental in that it leads to premature wear of the material, which may lead to its destruction. Summary of the invention

[0006] The invention overcomes these drawbacks by densifying the metal foam inside the hairpin bends.

[0007] For this purpose, the invention relates to an exhaust gas heating device for an exhaust line of an internal combustion engine, comprising a housing extending along an axis, over a length, a heating element, in the form of a wafer of metal foam having a thickness, housed in the housing and occupying the entire section of the housing, comprising substantially flat slots along a plane parallel to the axis, substantially parallel to each other, passing through the thickness, and extending over a length strictly less than the width of the heating element, a slot having a first end opening at the periphery of the heating element and a second end, alternating a first end on one side and a first end on the other side, from one slot to the other, the heating element comprising a densified material at the second ends.

[0008] Particular characteristics or embodiments, usable alone or in combination, are: - a densified material is obtained by injecting a molten metal at a second end, - the molten metal is made of the same material as the heating element, - a densified material is obtained by inserting a metal tube at a second end, - the metal tube is welded or clipped to the heating element, - the tube is split along its entire length, - the tube has a length greater than the thickness of the heating element, the excess length being preferably arranged on the upstream side of the device or even preferably arranged on both sides of the device, - the tube is made of the same material as the heating element.

[0009] In a second aspect of the invention, an exhaust line comprising at least one such device. Brief description of the drawings

[0010] The invention will be better understood on reading the following description, given solely by way of example, and with reference to the appended figures in which:

[0011] [fig. 1] figure 1 illustrates, in perspective view, a first embodiment of a device,

[0012] [fig.2] figure 2 illustrates, in exploded perspective view, another embodiment of a device,

[0013] [fig.3] figure 3 illustrates in sectional profile view, a heating element with molten metal,

[0014] [fig.4] figure 4 illustrates in sectional profile view, a heating element with tube. Description of the embodiments

[0015] With reference to Figure 1, an exhaust gas heating device 1 for an exhaust line of an internal combustion engine comprises a housing 2, substantially hollow cylindrical, extending along an axis X over a length Le. The cross-section of this housing 2 to the axis X may be of any shape. It may thus be oval. The example illustrated has a housing 2 of circular cross-section. The device 1 further comprises a heating element 4. This heating element 4 is a wafer of metal foam, advantageously flat. It has a thickness Ee at most equal to the length Le. It is housed in the housing 2, the entire cross-section of which it occupies. The exhaust gases pass through the housing 2 and pass through the heating element 4 in the direction of the thickness Ee.

[0016] The heating element 4 is heated by the Joule effect. Its metallic composition is used to advantage. An electric current, supplied by two electrodes 10, arranged for example on either side of the heating element 4, by its edge, circulates through the heating element 4. The latter, due to its electrical resistance, heats up.

[0017] In order to create this heat and distribute it to every point of the heating element 4, the longest possible electrical path is created, for example in the shape of a snake. This can be achieved by means of alternating slots 12. These slots 12 are made in the heating element 4 by any machining means: shears, laser machining, water jet machining, electroerosion, etc. The slots 12 thus form an insulator between the foam on either side of the slot 12. According to a possible embodiment, these slots 12 are substantially flat along a plane parallel to the axis X. They are substantially parallel to each other. They pass through the entire thickness Ee. The slots 12 extend over almost the entire width of the heating element 4 in line with a slot 12, i.e. along a length strictly less than the width of the heating element 4.Thus, for each slot 12, along an extension in a plane perpendicular to the X axis, a slot 12 has a first end 14 opening at the periphery of the heating element 4, i.e. close to the housing 2 and a second end 16, located in the material of the heating element 4. Each slot 12 alternates, with the next or previous slot, the direction of the slot 12: the first end 14, i.e. the opening end on one side, and the first end 14 of the previous or next slot 12, on the other side. This contributes to forming a path which winds through the entire volume of the heating element 4 and forms, in the plane perpendicular to the X axis, a snake, a succession of alternating zigzag turns or a boustrophedon. It is recalled here that a boustrophedon designates a continuous line alternately folded back on itself, changing direction with each fold, like furrows plowed in a field.

[0018] In order for the electric current to flow well in the electrical path described above, the heating element 4 is separated from the metal housing 2 by an electrical insulation means 8, here in two half-shells. Alternatively, the electrical insulation means 8 can be made in a single piece covering the total length of the two half-shells. The heating element 4 advantageously comprises two interface contacts 6 with each electrode 10. The assembly comprising the heating element 4 and the electrical insulation means 8 is held integral with the housing 2 by means of two holding elements 18, arranged on either side of the heating element 4. These holding elements 18 are annular. They can be identical or of different shapes from each other. They can comprise fixing lugs. Alternatively, they can comprise a peripheral edge comprising notches for the passage of the electrodes 10.

[0019] There appears, in a detrimental manner, at the level of each such lace, mainly in the interior of the lace, a concentration of electric current which causes an electrical and thermal hot spot.

[0020] In order to reduce, or even eliminate, these hot spots, present at each second end 16, it is desired to reduce the electrical resistance at these interior points of the loop or turning point 16 of the electrical path.

[0021] Also, for this, according to an important characteristic, the heating element 4 comprises a densified material 20, 22 at each second end 16. Indeed, an increase in the metallic material, locally at a turning point 16, reduces the electrical resistance and thus allows improved, easier circulation of the electric current in this turning point 16. This leads to less heating.

[0022] According to a first embodiment, more particularly illustrated in Figure 3, the densified material 20 is obtained by injecting a molten metal 20 at a second end 16. This injection is possible in that the foam constituting the heating element 4 is porous and allows the passage of the molten metal in liquid or pasty form. The injection is advantageously carried out on a column occupying the entire thickness Ee of the heating element 4. At the location where the molten metal 20 is injected, the density of the material increases significantly relative to the density of the initial foam. The molten metal 20 then hardens during solidification by cooling. The column of molten metal 20, once hardened, reinforces the structure of the heating element 4.

[0023] The insertion of molten metal 20 can be carried out either before or after the machining of the slots 12.

[0024] Advantageously, according to another characteristic, the molten metal 20 is made of the same material as the heating element 4, i.e. of the same material as the foam metallic 4. This notably facilitates the cohesion and electrical connectivity between the densified column 20 and the rest of the metallic foam 4.

[0025] According to another embodiment, alternative or complementary to the first embodiment, more particularly illustrated in FIG. 4, the densified material 22 is obtained by inserting a metal tube 22 at a second end 16. Advantageously, a tube 22 is inserted at each second end 16, i.e. at each turning point 16. In order to prepare and facilitate the insertion of a tube 22, a hole of the same diameter as the tube 22 is advantageously made in the metal foam 4. The diameter of the hole can still be slightly smaller in order to guarantee that the tube 22 is held in the metal foam 4.

[0026] According to another characteristic, in order to ensure cohesion and electrical connectivity, the metal tube 22 is preferably welded to the heating element 4. Alternatively or additionally, clipping can still be carried out.

[0027] According to another characteristic, the tube 22 can still be split, over its entire length Lt.

[0028] According to another characteristic, the tube 22 has a length Lt greater than the thickness Ee of the heating element 4. Also, the tube 22 protrudes from one face or both faces of the heating element 4. This is advantageous in that the tube 22, including with the protruding excess length D, participates in the heat exchanges with the exhaust gas, including before the heating element 4 and / or even after. If the excess length D is arranged on only one side of the heating element 4, the excess length D is preferably arranged on the upstream side of the device 1, marked by an arrow indicating the direction of travel of the exhaust gases, i.e. the side arranged at the top in FIG. 4.

[0029] The production of the hole preparing the insertion of a tube 22 in the foam of the heating element 4, creates, according to the machining method, a clearance cone visible in figure 4. Advantageously, this clearance cone is arranged on the upstream side so as to face the flow of exhaust gas.

[0030] Advantageously, according to another characteristic, a tube 22 is made of the same material as the heating element 4, i.e. of the same material as the metal foam. This facilitates in particular the cohesion and the electrical connectivity between the tube 22 and the rest of the metal foam 4.

[0031] The invention also relates to an exhaust line comprising at least one such device 1.

[0032] The invention has been illustrated and described in detail in the drawings and the preceding description. This should be considered as illustrative and given by way of example and not as limiting the invention to this description alone. Numerous alternative embodiments are possible. List of reference signs

[0033] 1: device,

[0034] 2: housing,

[0035] 4: heating element,

[0036] 6: contact,

[0037] 8: electrical insulation means

[0038] 10: electrode,

[0039] 12: slot,

[0040] 14: first end (opening),

[0041] 16: second end (non-opening),

[0042] 18: holding element,

[0043] 20: molten metal,

[0044] 22: tube,

[0045] D: over-length,

[0046] Ee: thickness of the heating element,

[0047] The: length of the case,

[0048] Lt: length of a tube,

[0049] X: axis

Claims

Claims

1. Exhaust gas heating device (1) for an exhaust line of an internal combustion engine, comprising, - a housing (2) extending along an axis (X) over a length (Le), - a heating element (4), in the form of a metal foam wafer having a thickness (Ee), housed in the housing (2) and occupying the entire section of the housing (2), comprising slots (12) substantially flat along a plane parallel to the axis (X), substantially parallel to each other, passing through the thickness (Ee), and extending over a length strictly less than the width of the heating element (4), a slot (12) having a first end (14) opening at the periphery of the heating element (4) and a second end (16), alternating a first end (14) on one side and a first end (14) on the other side, from one slot (12) to the other, characterized in that the heating element (4) comprises a densified material (20,22) at the second ends (16).,

2. Device (1) according to the preceding claim, where a densified material (20) is obtained by injecting a molten metal (20) at a second end (16).

3. Device (1) according to the preceding claim, where the molten metal (20) is made of the same material as the heating element (4).

4. Device (1) according to any one of the preceding claims, wherein a densified material (22) is obtained by inserting a metal tube (22) at a second end (16).

5. Device (1) according to the preceding claim, where the metal tube (22) is welded or clipped to the heating element (4).

6. Device (1) according to any one of the two preceding claims, wherein the tube (22) is split, over its entire length (Lt).

7. Device (1) according to any one of the three preceding claims, where the tube (22) has a length (Lt) greater than the thickness (Ee) of the heating element (4), the excess length (D) being preferentially arranged on the upstream side of the device (1) or even preferentially arranged on both sides of the device (1).

8. Device (1) according to any one of the four preceding claims, wherein the tube (22) is made of the same material as the heating element (4).

9. Exhaust line characterized in that it comprises at least one device (1) according to any one of the preceding claims.

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