LIGHTWEIGHT FLOW HEAT EXCHANGER

Abstract

A heat exchanger is disclosed for the exhaust gas train of a motor vehicle with an exhaust gas carrying exchanger tube that is formed separately and is disposed in a closed housing formed separately, a coolant flowing through the housing and around the outer side of the exchanger tube. The housing forms at least one housing cover and one housing case, the housing case being tightly closed by the housing cover. Both ends of the exchanger tube are conducted for gas and liquid tight connection through the housing cover so that the inlet and the outlet of the exchanger tube are disposed outside of the housing.

Claims

1. A heat exchanger for an exhaust gas system of a motor vehicle comprising: a closed housing including at least one housing cover and one housing case, wherein the housing case is enclosed by the housing cover; and an exhaust gas carrying exchanger tube disposed in the housing, an outer surface of the exchanger tube forming a substantially fluid tight seal with the housing and a first end and a second end of the exchanger tube are disposed outside of the housing, wherein a coolant flows through the housing and around an outer surface of the exchanger tube.

2. The heat exchanger as set forth in claim 1, wherein the exchanger tube is made from a corrosion and heat resistant, substantially flexible material.

3. The heat exchanger as set forth in claim 1, wherein the housing cover is produced from a material of the same material as the exchanger tube.

4. The heat exchanger as set forth in claim 1, wherein the housing case is produced from one of a castable material and a material that is deep-drawn.

5. The heat exchanger as set forth in claim 1, wherein the housing case is formed as a cast part.

6. The heat exchanger as set forth in claim 1, wherein a seal is disposed between the housing case and the housing cover.

7. The heat exchanger as set forth in claim 6, wherein the seal is produced from an elastic material.

8. The heat exchanger as set forth in claim 1, wherein the housing cover and the housing case are separate parts joined together by means of mechanical retaining means.

9. The heat exchanger as set forth in claim 1, wherein the housing cover forms an interface for connecting the heat exchanger to the exhaust gas system of the motor vehicle.

10. The heat exchanger as set forth in claim 1, wherein the exchanger tube is substantially made from one piece between points at which the exchanger tube forms a seal with the housing.

11. The heat exchanger as set forth in claim 1, wherein the exchanger tube is curved in a substantially U-shape between points at which the exchanger tube forms a seal with the housing.

12. The heat exchanger as set forth in claim 1, further comprising a plurality of exchanger tubes disposed in the housing, the tubes forming a bundle connected in parallel in terms of fluid flow.

13. The heat exchanger as set forth in claim 12, wherein the flow paths of the exchanger tubes have no contact to each other between respective inlets and outlets.

14. The heat exchanger as set forth in claim 1, wherein the exchanger tube is a smooth-walled tube.

15. The heat exchanger as set forth in claim 1, wherein the exchanger tube is a swirl tube.

16. The heat exchanger as set forth in claim 15, wherein the heat exchanger tube is widened in spirals.

17. The heat exchanger as set forth in claim 16, a winding distance of the spirals is between 1 and 15 millimeters.

18. The heat exchanger as set forth in claim 16, wherein a depth of the spirals is between 1 and 20% of an outer diameter of the exchanger tube.

19. The heat exchanger as set forth in claim 1, wherein a flow path extends in the exchanger tube, the flow path running as a winding flow path at least inside the housing and including an angle of rotation of at least 135.

20. The heat exchanger as set forth in claim 1, wherein the exchanger tube has an outer diameter between 1 and 15 millimeters.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The above, as well as other objects and advantages of the invention, will become readily apparent to those skilled in the art from reading the following detailed description of a preferred embodiment of the invention when considered in the light of the accompanying drawing which:

[0035] FIG. 1 shows an exploded view of a first exemplary embodiment of an exhaust gas heat exchanger of the invention;

[0036] FIG. 2 is an elevation view of the mounting interface E of an exhaust gas heat exchanger according to a second exemplary embodiment;

[0037] FIG. 3 is an elevation view of a bundle of exchanger tubes of an exhaust gas heat exchanger according to a third exemplary embodiment;

[0038] FIG. 4 is a schematic illustration of an exchanger tube of the heat exchanger shown in FIG. 1;

[0039] FIG. 5 is a sectional view through the exchanger tube shown in FIG. 4;

[0040] FIG. 6 is a schematic view of an exchanger tube that forms a winding flow path for illustrating the revolution angle ;

[0041] FIG. 7 is an elevation view of the interface E formed by one housing cover in which the inlet and outlet openings are disposed on grid places of an orthogonal grid;

[0042] FIG. 8 is an elevation view of the interface E formed by one housing cover in which the inlet and outlet openings are disposed on grid places of a hexagonal grid;

[0043] FIG. 9 is a sectional view through an inlet/outlet opening of an exchanger tube in the region of a housing cover; and

[0044] FIGS. 10a-10g show swirl tubes that are suited for use in a heat exchanger of the invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

[0045] The following detailed description and appended drawings describe and illustrate various embodiments of the invention. The description and drawings serve to enable one skilled in the art to make and use the invention, and are not intended to limit the scope of the invention in any manner. In respect of the methods disclosed, the steps presented are exemplary in nature, and thus, the order of the steps is not necessary or critical.

[0046] FIG. 1 shows an exploded view of an exhaust gas heat exchanger 1 according to a first exemplary embodiment. The heat exchanger 1 includes housing 40 that consists of a housing case 50 which is closed by means of a housing cover 60. The housing case 50 is configured to be a cast part and may be made from aluminium die casting in particular. Alternatively, the housing case 50 in the exemplary embodiment shown may be made from any material that can be processed by casting on the one side and that has sufficient thermal stability on the other side. Since the housing case 50 of the heat exchanger 1 of the invention only comes into touching contact with the coolant usually originating from the coolant circuit of the motor vehicle, a resistance to temperatures of up to 150 C. is sufficient for most of the cases of application. Magnesium or magnesium alloys, gray cast iron or also heat resistant and die-castable plastic materials have been found to be further materials suited for the housing case.

[0047] On the front side, the housing case 50 forms a flange 59 for connection to a housing cover 60. In the exemplary embodiment shown, the housing cover 60 consists of a punched steel plate having a thickness of a few millimeters, preferably of approximately 1-2 mm. The housing case 50 is connected for liquid and gas tight connection to the housing part 60, a seal 52, which, in the exemplary embodiment shown, is configured to be a metal bead seal, being inserted therein between. The housing cover 60 is thereby screwed to the flange 59 of the housing case 50 by means of screws 54. For this purpose, the housing case 50 forms a plurality of large threaded holes 55. At the corresponding positions, the housing cover 60 comprises through holes 65 of large diameter through which screws 54 of mating dimensions are threaded and inserted into the threaded holes 55 for the housing cover 60 to be screwed to the housing case 50.

[0048] The housing case 50 forms an inner volume 42 that is provided for accommodating therein a bundle of U-shaped exchanger tubes 20. The exchanger tubes 20 are identical with respect to their dimensions such as inner and outer diameter, but the opening width W (see FIG. 4) of the U-shaped profile varies. The shape of the inner volume 42 and as a result thereof of the housing case 50 is generally adapted to the shape of the bundle of exchanger tubes 20 so that the bundle of exchanger tubes allows for using most efficiently the space in the inner volume 42.

[0049] At their respective ends, the exchanger tubes 20 each form an inlet 22 and an outlet 24. The ends of the exchanger tubes 20 are thereby conducted through corresponding holes in the housing cover 60, which form the passage points 66, 68 for the inlets 22 or the outlets 24 of the exchanger tubes 20. The inlets and outlets 22, 24 of the exchanger tubes 20 are thereby conducted through the holes formed in the housing cover 60. At the passage points 66, 68, the exchanger tubes 20 are connected for gas and liquid tight connection to the housing cover 60 such as by soldering or welding. As a result, the exchanger tubes 20 mechanically abut the housing cover 60.

[0050] In an embodiment, the exchanger tubes 20 consist of thin-walled stainless steel tubes. The exchanger tubes 20 are thereby provided with a stamped structure so that a raised spiral-shaped structure 26 is formed on the inner surface of the exchanger tubes 20. The bundle of exchanger tubes 20 is thereby disposed so that all the inlets 22 and all the outlets 24 are respectively arranged in one cohesive group for ease of connection of the heat exchanger 1 of the invention to the exhaust gas system of the motor vehicle for example. For this purpose, the front side of the housing cover 60 forms an assembly interface S that is configured in a substantially flange-like fashion due to the planar configuration of the housing cover 60. For mounting the heat exchanger 1 to the motor vehicle, further threaded holes 53 are formed in the housing case 50, said holes having a smaller diameter compared to the threaded holes 55. In the metal bead seal 52 as well as in the housing cover 60 there are formed corresponding through holes 63. Via these holes, the heat exchanger 1 can be connected to the exhaust gas and coolant system of the motor vehicle through a plurality of screws, which have not been illustrated in FIG. 1.

[0051] Beside the inner volume 42 accommodating the bundle of exchanger tubes 20, the housing case 50 forms an inlet channel 56 and an outlet channel 58 for a coolant; said coolant can be a cooling liquid from the cooling system of the internal combustion engine of the motor vehicle. The inlet channel 56 and the outlet channel 58 are thereby arranged for a flow path extending from the top to the bottom (in FIG. 1) to form through the inner volume 42 of the housing case 50 when the heat exchanger 1 is operated according to the use it was intended for so that the bundle of exchanger tubes 20 is intensively flooded by the coolant. In order to achieve as intensive as possible an interaction between the coolant and the surface of the exhaust gas carrying exchanger tubes 20, a baffle plate 36 is disposed within the legs of the U-shaped exchanger tubes 20, said baffle plate being again preferably made from stainless steel in the exemplary embodiment shown and being butt soldered or butt welded to the housing cover 60 also made from stainless steel. The baffle plate 36 lengthens the flow path of the coolant in the inner volume 42 of the housing 40, thus ensuring a more intensive thermal exchange between the exhaust gas flowing in the exchanger tubes 20 and the coolant flowing in the inner volume 42.

[0052] The inlet channel 56 as well as the outlet channel 58 formed in the housing case 50 also end in the flange 59 formed by the housing case 50, webs 57 being formed at the ends of the channels 56 and 58 for forming a mechanical abutment for the metal bead seal 52 resting on the flange 59. Said seal also forms passageways for the coolant flowing through the heat exchanger 1, which correspond to the coolant inlet 62 and the coolant outlet 64 formed in the housing cover 60. In the assembled heat exchanger 1, coolant can be both supplied through the coolant inlet 62 and evacuated through the coolant outlet 64 and the combustion exhaust gas to be cooled can be supplied through the inlets 22 of the exchanger tubes 20 and evacuated through the outlets 24 via the front side of the housing cover 60. In the construction shown, this is possible through one single common mounting interface S.

[0053] This is particularly obvious from the illustration shown in FIG. 2 which shows an elevation view of a mounting interface S of the heat exchanger 1 in a slightly altered embodiment. The coolant inlet 62 formed in the housing cover 60 and the coolant outlet 64 are clearly visible. By contrast, the majority of inlets 22 and outlets 24 of the exchanger tubes 20 are covered by grid structures 23 in the illustration shown in FIG. 2. The arrangement of the inlets 22 and of the outlets 24 in the housing cover 60 substantially corresponds to the configuration shown in FIG. 1. For the rest, the heat exchanger shown in the illustration of FIG. 2 substantially differs by the modified arrangement of fastening points 51 to the housing case 50, these fastening points 51 serving to fasten the heat exchanger 1 to mounting structures of the motor vehicle.

[0054] FIG. 3 shows a perspective illustration of a bundle of exchanger tubes 20 of a heat exchanger 1 in a third implementation. As compared to the heat exchanger 1 shown in FIG. 1, the bundle of exchanger tubes 20 shown herein substantially differs by the fact that the exchanger tubes 20 are smooth, e.g., seamless drawn thin-walled stainless steel tubes that have no spiral-shaped structure 26 like the one shown in FIG. 1. Furthermore, the exchanger tubes 20 are arranged so as to intersect by pairs, this being visible at the inversion points of the U-shaped exchanger tubes 20 in FIG. 3.

[0055] In FIG. 1 it can be further seen how undesirable oscillations of the bundle of exchanger tubes 20 in the inner volume 42 of the housing 40 can be prevented by means of technical measures. The baffle plate 36, which is connected for mechanical rigid connection to the housing cover 60 and is disposed within the bundle of exchanger tubes 20, is connected at its side wall and at its bent tip to the neighboring exchanger tubes 20 such as by soldering or welding for a mechanical solid connection. The baffle plate 36 thus mechanically stiffens the exchanger tubes 20 of the exchanger tube bundle lying inside, thus attenuating their oscillations.

[0056] As an additional measure to reduce the oscillations there is provided a bandage 30 made from a stamped stainless steel sheet of small wall thickness. This bandage completely surrounds the bundle of the exchanger tubes 20 and is connected at the contact points to the neighboring exchanger tubes 20 for mechanical solid connection such as by means of welding or soldering. Thanks to the arrangement surrounding the bundle of exchanger tubes, the bandage 30 prevents relative oscillations of the outside lying exchanger tubes 20 relative to each other. Moreover, the bandage 30 forms integrally formed abutments 32 that consist of angled projections. These abutments 32 resiliently support the entire bundle of exchanger tubes with respect to the inner wall of the housing 40.

[0057] Finally, stiffening elements 34 are arranged within the bundle of exchanger tubes 20, which also are made from stamped stainless steel strips. These stiffening elements 34 constitute a mechanically rigid abutment of the exchanger tubes 20 of the bundle of exchanger tubes. For this purpose, they are connected to the exchanger tubes 20 for mechanical solid connection such as by means of welding or soldering.

[0058] It is noted that the mechanical solid connection of the bandage 30 or of the stiffening elements 34 to the discrete exchanger tubes 20 can be eliminated. Possibly, the mere interlock between the bundle of exchanger tubes and the bandage 30 or the stiffening element 34 may already provide for sufficient abutment of the bundle of exchanger tubes and for the bandage 30 or the stiffening elements 34 to sit sufficiently solidly on the bundle of exchanger tubes.

[0059] FIG. 4 now shows an elevation view of one exchanger tube 20 of the heat exchanger 1 according to the first exemplary embodiment. The exchanger tube 20 has a free length indicated at L that can range between 2 and 30 cm depending on the dimensions of the heat exchanger 1; if used in motor vehicles with an internal combustion engine of less output (typically 35-100 kW), appropriate typical dimensions of L are of about 5 cm. For private cars of higher output of 100 kW and more, dimensions of L ranging between 10 and 15 cm may be sensible. For use in trucks, dimensions of L=20 cm and more may be suited.

[0060] The exchanger tube 20 has an outer diameter D that typically ranges between 1 and 15 mm, preferably between 6 and 12 mm, since this diameter has been found particularly suited for using the heat exchanger in accordance with its purpose of utilization as an exhaust gas heat exchanger for a motor vehicle. As can be seen in FIG. 4 and in FIG. 5, which constitutes a perspective sectional view of the exchanger tube 20 of FIG. 4, values ranging from 0.1 to 1 mm are suited for the wall thickness WS of the exchanger tubes 20, depending in particular also on the length L of the exchanger tube 20 in the specific heat exchanger 1. Preferably, the wall thickness WS of the exchanger tubes 20 ranges from 0.2 through 0.6 mm.

[0061] For the spacing W between the legs of the U-shaped exchanger tubes 20, it has been found out that this spacing is preferably greater than or equal to 1.8 times the outer diameter D of the exchanger tube 20. The following applies in particular. W is greater than or equal to 1.8D, and it has been found out that the leg width W, which is directly correlated to the bending radius R of the U-shaped exchanger tube 20, is greater than W=2R, if the exchanger tube 20 used is a thin-walled tube, for example made from stainless steel or aluminium, provided with a continuous spiral structure 26. A particularly small leg width W is of benefit for most efficient possible occupancy of the inner volume of the housing 40 and is to be preferred due to the very limited space available in a motor vehicle.

[0062] Within the frame of practical testing it has been found out that particularly advantageous properties with respect to generating a turbulence in the exhaust gas flowing through the exchanger tube 20 and as a result thereof a particularly intensive heat transfer from the exhaust gas to the wall of the exchanger tube are achieved if the exchanger tube 20 comprises a spiral structure 26 at least on its inner wall. The spacing DS between the windings of the spiral structure 26 advantageously ranges between 1 and 15 mm, with a range of between 4 and 8 mm being preferred. The resulting pitch is indicated at DW in FIG. 4. The height DT of the raised spiral structure 26 on the inner wall of the exchanger tube 20 advantageously ranges between 1 and 20% of the outer diameter D of the respective exchanger tube 20, with a range of between 2.0 and 14% being preferred here.

[0063] If a plurality of exchanger tubes 20 is provided for a bundle of exchanger tubes to form, it has been found out that the efficiency achievable if the heat exchanger is used according to its purpose of utilization is particularly high if the minimum distance d between the outer surfaces of the respective exchanger tubes 20 of the bundle of exchanger tubes ranges between 0.5 and 5 mm. A range of between 1 and 2 mm is preferred here, since it yields particularly good results with respect to efficiency if water is used as the coolant.

[0064] In an embodiment of the invention, the spiral structure 26 in the exchanger tube 20 is not only formed on the inner surface of the exchanger tube 20. Instead, the spiral structure 26 is produced by stamping a spiral shape into the outer surface of the exchanger tube 20, which results in a stamped raised spiral structure 26 on the inner surface of the exchanger tube 20.

[0065] FIG. 6 schematically shows the angle of rotation that is surrounded by the flow path forming in the exchanger tube 20. In the preferred embodiments of the heat exchanger 1 of the invention, this angle of rotation =180, i.e., the flow direction of the exhaust gas flow exiting the inner volume 42 of the heat exchanger 1, is 180 opposite the flow direction of the entering exhaust gas flow. In other configurations, the angle of rotation may however be smaller or greater than 180, an angular range of between 135 and 225 being generally preferred. The use of exchanger tubes 20 forming a spiral structure 26 on their inner surface has already been found to increase efficiency at an angle of rotation of 45.

[0066] FIG. 7 schematically shows once more an elevation view of the inlets 22 and the outlets 24 of a plurality of exchanger tubes 20 that are arranged in a bundle in the inner volume 42 of a heat exchanger housing 40. It appears that both the inlets 22 and the outlets 24 are disposed on the grid points of an orthogonal grid.

[0067] An even more efficient space occupancy is obtained if the inlets 22 and outlets 24 are arranged as shown in FIG. 8. Here, the inlets 22 or outlets 24 are disposed on grid points of a hexagonal grid, which means that each inlet 22 or each outlet 24 is surrounded by six neighboring inlets 22 or outlets 24. In this configuration, the space inside the inner volume 42 of the housing 40 can be best used for the exchanger tubes 20.

[0068] FIG. 9 shows a sectional view of a housing cover 60 in the region of a hole through which the inlet or outlet side end 22/24 of an exchanger tube 20 is threaded. In a preferred implementation, which offers particular advantages for manufacturing, the exchanger tube 20 comprises at its inlet or outlet side end 22/24 a supporting structure 27 that forms a mechanical abutment of the tube end with respect to the housing cover 60. This supporting structure may for example be formed from one or several dot-shaped projections, in the exemplary embodiment shown in FIG. 4 it is stamped as a circumferential bulge. In the exemplary embodiment shown in FIG. 9, the outer end of the exchanger tube 20 is beaded so that, generally, the exchanger tube 20 mechanically abuts the housing cover 60 through the combination of supporting structure 27 and beaded end. This abutment substantially facilitates the manufacturing of the heat exchanger of the invention since the exchanger tubes 20 are already pre-fixed mechanically in the housing cover 60. This dispenses with the need for additionally fixing the exchanger tubes 20 to the housing cover 60 such as by means of laser welding spots during subsequent soldering or welding of the exchanger tube ends to the housing cover 60. The structures shown in FIG. 9 may be made in the simplest way in the exchanger tube end by threading an exchanger tube 20 with uniform inner and outer diameter through the corresponding hole in the housing cover 60. After that, the circumferential bulge 27 and at the same time the beaded edge is produced using an appropriate tool. This appropriate tool is for example a tube expansion tool.

[0069] The sequence of the FIGS. 10 a through g finally shows by way of example a selection of swirl tubes the structure of the inner surface of which is suited for creating a turbulence in the exhaust gas flow flowing inside, in particular, if the flow path forming the at least one exchanger tube 20 of the heat exchanger 1 made from the swirl tube has an included angle of more than 45, in particular of 180. FIG. 10 a shows once more the spiral structure shown in FIG. 5, which has a constant pitch and a constant structure height DT and is formed in a tube 20 having a constant cross section over its length.

[0070] FIG. 10 b shows a swirl tube having two substantially identical spiral structures, wound however in opposite directions. Except for a reduced pitch, each of the two spiral structures corresponds to the spiral structure shown in FIG. 5. Also, the cross section of the tube is substantially constant over its entire length.

[0071] FIG. 10 c shows a swirl tube in which the cross section of the tube tapers/widens over its length. The spiral structure itself again substantially corresponds to the structure shown in FIG. 5.

[0072] By contrast, in the swirl tube shown in FIG. 10 f, the cross section of the tube is again substantially constant over its entire length whilst the pitch of the spiral structure varies over the length of the tube.

[0073] FIG. 10 d shows an alternative to the spiral structures of the other structure examples, namely planar circular depressions in the wall of the tube, which result in circular raised structures on the inner wall of the tube. Instead of planar circular depressions, annular depressions may also be formed in the wall.

[0074] The turbulence structure shown in FIG. 10 e is not spiral-shaped either; instead, the tube wall is annularly deformed at even intervals, thus resulting in regular constrictions on the inner wall. Over the length of the tube, the depth of the constrictions and/or their spacing may be varied.

[0075] FIG. 10 g finally shows a swirl tube with a substantially constant cross section in the wall of which there is formed a plurality of identical spiral structures having a constant pitch and structure height.

[0076] To conclude, it is noted that the turbulence structures shown in the FIGS. 10 a through g can not only be utilized isolated, but may be freely combined together if technically practicable. The structure features of the FIGS. 10 a through c as well as f and g in particular can be advantageously combined together.

[0077] From the foregoing description, one ordinarily skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications to the invention to adapt it to various usages and conditions.