Heat exchanger for cooling exhaust gas and method of manufacturing same

A heat exchanger for cooling exhaust gas, around which liquid cooling medium flows on the outside, including a bundle of rectangular tubes provided as ducts for the exhaust gas whose ends are welded into tube bottoms. The bundle of rectangular tubes is surrounded with a sheet metal jacket which follows the contour of the bundle and which is provided with a cooling medium inlet and a cooling medium outlet. The ends of the sheet metal jacket are provided with welded-on flange plates which are each open by means of a central opening with respect to the bundle of rectangular tubes and which are provided with fastening devices for fastening onto pipe sections of an exhaust pipe.

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to a heat exchanger for cooling exhaust gas of an internal-combustion engine having a plurality of ducts for guiding the exhaust gas which are provided with lugs arranged in pairs diagonally to the flow, direction and projecting from at least one wall of the ducts, and a liquid cooling medium flowing on the outside around the ducts. This invention also relates to a method of manufacturing such a heat exchanger.

In the case of a known heat exchanger of the initially mentioned type, the ducts are formed of disk-shaped heat exchange elements between which one turbulence insert respectively is arranged which has lugs which are arranged in pairs and extend diagonally to the flow direction. This heat exchanger known from German Patent Document DE-U 94 06 197.1 fulfills its task satisfactorily. However, considerable expenditures are required to implement heat exchangers of different sizes for different vehicles because the individual elements must then be manufactured with accurate measurements in the different sizes.

It is an object of the invention to provide a heat exchanger of the initially mentioned type which can be manufactured in different sizes, in which case no excessively high variations in dimension must be maintained for the individual structural elements.

This and other objects have been achieved according to the present invention by providing a bundle of rectangular tubes as ducts for the exhaust gas whose ends are welded into latticed tube bottoms, wherein the bundle of rectangular tubes is surrounded by a sheet metal jacket which follows the contour of the bundle, is provided with a cooling medium inlet and a cooling medium outlet and is welded to the tube bottoms, and wherein the ends of the sheet metal jacket are provided with welded-on flange plates which are open with respect to the bundle of rectangular tubes by way of a central opening and which are provided with fastening devices for attachment with pipe sections of an exhaust gas pipe.

This and other objects have been achieved according to the present invention by providing a heat exchanger for cooling exhaust gas of an internal-combustion engine, comprising a plurality of tubes for guiding exhaust gas; first and second latticed tube bottoms, each tube bottom defining a plurality of openings corresponding to an outer periphery of respective of the tubes, first and second axial ends of each of the tubes being arranged in respective of the openings in the first and second tube bottoms such that the tube bottoms support the tubes substantially parallel to one another and spaced-apart from one another in a bundle; a sheet metal jacket concentrically surrounding the bundle and attached to the tube bottoms, the sheet metal jacket and the tube bottoms defining a chamber, the sheet metal jacket being provided with a coolant inlet and a coolant outlet to allow a liquid coolant to enter the chamber, flow around an exterior surface of the tubes in the chamber, and exit the chamber; and flange plates attached to ends of the sheet metal jacket and configured for attachment to an exhaust pipe, each the flange plate defining an opening which communicates an interior of the tubes with an interior of the exhaust pipe.

This and other objects have been achieved according to the present invention by providing a method of manufacturing a heat exchanger for cooling exhaust gas of an internal-combustion engine, the method comprising the steps of: providing a plurality of rectangular tubes for guiding exhaust gas; attaching a plurality of lugs to the rectangular tubes diagonally to a flow direction of the exhaust gas, the lugs being arranged in pairs; attaching ends of the rectangular tubes to the latticed tube bottoms such that the rectangular tubes form a bundle; attaching a sheet metal jacket to the tube bottoms and around the bundle; providing the sheet metal jacket with a coolant inlet and a coolant outlet to allow a liquid coolant to flow around the rectangular tubes in the sheet metal jacket; and attaching flange plates to ends of the sheet metal jacket, the flange plates being configured for attachment to an exhaust pipe, each the flange plate defining a central opening which communicates the rectangular tubes with the exhaust pipe.

The heat exchanger according to the present invention essentially comprises sheet metal components which can be manufactured in a simple manner, for example by welding. Welding is preferably carried out by laser welding or micro TIG welding. The latticed tube bottoms, which-may be stamped out of a steel plate, have openings corresponding to the number and arrangement of the rectangular tubes. In certain preferred embodiments, the thickness of the steel plate is approximately 1 mm to 3 mm. The distances between the rectangular tubes, and correspondingly the web width of the tube bottoms, vary according to the desired mass flow rate of the coolant. In certain preferred embodiments, these distances are approximately 1 mm to 3 mm. The outer contour of the tube bottoms depends upon the number and the arrangement of the flat tubes. The sheet metal jacket also may be made in a simple manner from a steel plate which has a sheet metal thickness which is similar to the tube bottoms. The sheet metal jacket can be edged in a simple manner in steps corresponding to the contour of the tube bottoms. The flange plates, which are provided with fastening devices, permit in a simple manner an arrangement of the heat exchanger between two pipe sections of an exhaust pipe, for example, in a manner similar to the arrangement of a catalyst.

In a further development of the invention, the rectangular tubes are each formed by two tube shells which are welded together. The lugs existing in pairs can be fastened directly to the rectangular tube or can be a component of this rectangular tube. However, they can-also be a component of inserts arranged in the rectangular tubes.

In a further development of the invention, the flange plates are provided with threaded sleeves in mutually essentially diametrically opposite areas. As a result, the flange plates may be screwed to mating flanges of a pipe section in an exhaust pipe in a simple manner.

In an advantageous further development of the invention, the sheet metal jacket is provided with a cooling medium inlet in the proximity of the flange plate which is in the front in the flow direction of the exhaust gas and is provided with a cooling medium outlet in the proximity of the rear flange plate. As a result, the cooling medium is guided through the heat exchanger in a co-current flow with the exhaust gas. Thus, the risk of a vapor formation on the inlet side of the exhaust gas is reduced because here the cooling medium has the relatively lowest temperature.

In a further development of the invention, the cooling medium inlet and the cooling medium outlet are arranged on opposite sides of the sheet metal jacket. Because of this arrangement, the flow paths of the individual current routes for the cooling medium around the rectangular tubes essentially have the same length ensuring a uniform flow around these rectangular tubes.

In a further development of the invention, the sheet metal jacket is composed of two preformed sheet metal shells which adjoin the tube bottoms by means of joint connections. After being welded together, the two sheet metal shells form a stiff and pressure-resistant housing. The joint connections provide the advantage that the elements to be welded together have a certain cohesion already before being welded, so that the welding operation can be carried out in a relatively simple manner.

For the same purpose, in a further development of the invention the flange plates adjoin the sheet metal jacket by means of joint connections. Furthermore, it is provided for the same purpose that the threaded sleeves adjoin the flange plates by means of a joint connection. As a result, the welding operation can be carried out in a relatively simple manner.

These and other objects, features and advantages of the present invention will become more readily apparent from the following detailed description when taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE DRAWINGS

The heat exchanger illustrated inFIGS. 1 and 2has a bundle of flat tubes10which have a wall thickness of, for example, approximately 0.3 mm to 0.4 mm. The ends of the rectangular tubes10are fitted into latticed tube bottoms11and are welded to them. Such a tube bottom11, which is used for receiving 16 rectangular tubes, is shown, for example, inFIG. 7. These tube bottoms11are stamped out of a steel plate which have a plate thickness in the order of, for example, from 1 mm to 3 mm. The webs between the openings which are used for receiving the flat tubes have a width which corresponds to approximately the wall thickness of the rectangular tubes10. Due to the width of the webs between the openings of the tube bottoms11, the rectangular tubes10are spaced apart from each other when arranged in an assembled position in the respective tube bottoms11. This spaced configuration allows a cooling medium to flow around each of the tubes throughout the axial length of the tubes between the respective tube bottoms11. The arrangement of the openings and thus of the webs of the tube bottoms11is selected such that in a rough approximation a circular or oval cross-section is created. The webs which surround the exterior rectangular tubes also have the same web width so that the outer contour of the tube bottoms corresponds to the contour of the tube bundle—enlarged by the web width.

The tube bottoms11are attached, for example welded, to the ends of a sheet metal jacket12which is indicated also inFIG. 7by a broken line. The sheet metal jacket12consists of two half shells made of steel plate which has a thickness corresponding essentially to the thickness of the tube bottoms11. The half shells are shaped corresponding to the outer contour of the tube bottoms11, and are, for example, edged or made by means of a high-pressure deformation process. The two half shells of the sheet metal jacket12are connected with one another, for example by longitudinal weld seams13. As illustrated inFIG. 7, the tube bottoms11are provided with a total of four slightly widened projections14, which define corresponding recesses for engagement with the ends of the two half shells of the sheet metal jacket12, effectively creating a joint connection.

Flange plates15are connected, for example welded, to the two ends of the sheet metal jacket12. The flange plates15may also be stamped from sheet metal and have a plate thickness which is similar to the plate thickness of the tube bottoms11. The flange plates15protrude in two diametrically opposite areas laterally over the contour of the sheet metal jacket. In this area, the sheet metal jacket12has projections which are lengthened in the axial direction beyond the tube bottoms11and is fitted by means of these lengthened projections into slot-shaped recesses17of the flange plates15. In this area, the sheet metal jacket12is connected to the flange plates15, for example by welding from the direction of the exterior side of the flange plates and/or welding from the other side.

As illustrated particularly inFIG. 2, the flange plates15have central, preferably circular recesses18whose dimensions correspond to the adjoining pipe sections of an exhaust system of a vehicle which are not shown.

In the diametrically opposite areas which project beyond the sheet metal jacket12toward the outside, the flange plates15are provided with threaded sleeves19,20. By means of a collar situated on their open sides, the threaded sleeves19are fitted into bores of the flange plates15and are connected together with them, for example by welding from the direction of the respective exterior side of the flange plates15. In the area of their closed side, the threaded sleeves19have a collar by means of which they are fitted into a holding web21. This holding web21is connected, for example welded, to the threaded sleeves19and to the sheet metal jacket12.

The threaded sleeves20illustrated inFIG. 8, which are provided with collars22on their open sides assigned to the flange plates15, are provided with collars23on their closed sides by means of which they are in each case fitted into a connection pipe24. The connection pipe24and the threaded sleeve20are connected to one another, for example by welding along a weld seam25. The exterior side of the weld seam25is ground down. Then a lateral recess26is milled into the connection pipe24. The threaded sleeves20are connected, for example welded, with their collar23into recesses of the flange plates15and are connected, for example welded, to the flange plates15. The connection pipes24are, in addition, connected, for example welded, by means of holding webs27to the sheet metal jacket. The respective outer edges of the holding webs27extend tangentially with respect to the connection pipe24to a plane surface of the sheet metal jacket. They are covered by cover plates28which are connected, for example welded, to the sheet metal jacket12, the holding webs27, the connection pipe24, the threaded sleeves20and the flange plate15. Thus, in the area of the recesses26between the holding webs27and the flange plates15, a type of water chamber is formed in the area of which the sheet metal jacket is provided with an inlet opening.

As illustrated inFIG. 1, the connection pipes24and the water chambers connected therewith are situated on mutually opposite sides of the sheet metal jacket so that an approximately Z-shaped flow path is provided for the cooling medium marked with the arrows29. In the area of all rectangular tubes10, this flow path has approximately the same flow route so that a very good and uniform flow around the rectangular tubes10takes place. As also illustrated inFIG. 1, the coolant inlet (top ofFIG. 1) is arranged on the side on which the inlet of the exhaust gas indicated with the arrow30is also situated while the coolant outlet is situated on the outlet side of the exhaust gas indicated by the arrow31. The cooling medium and the exhaust gas therefore flow in a co-current flow inside the heat exchanger.

As illustrated inFIG. 1and explained further inFIGS. 3 to 6, the rectangular tubes are equipped with lugs which are arranged in pairs. The lugs project in each case away from opposite walls toward the inside and are arranged diagonally with respect to the flow direction of the exhaust gas in such a manner that they diverge from a narrowest point at an angle, for example at approximately 40°. The rectangular tubes are each welded together from two tube shells10′ which are connected, for example welded, to one another on their respective narrow sides. The tube shells have a plate thickness of approximately 0.3 mm to 0.4 mm. The lugs32have approximately the same thickness and a length of approximately ten times their plate thickness. They diverge from a narrowest point, at which they have a distance of approximately 1.2 mm from one another, at an angle of 40°. The height of the lugs32amounts to approximately one-fourth to one-third of the overall height of the flat tubes. In the embodiment according toFIGS. 3aand3b, the tube halves10′ are provided with slots into which the lugs32are inserted and are then welded to the tube halves10′ as shown inFIG. 3c. In order to avoid seal welding, the lugs32can be provided with one or several elevations on their side facing the tube halves10′ so that they are welded to the tube halves10′ by means of the known stud welding technique.

In the illustrated embodiment according toFIGS. 3a,3b, the lugs32of the two tube halves are arranged opposite one another. In a modified embodiment, the lugs32of the two tube halves10′ are arranged eccentrically in such a manner that the lugs32of the upper tube half and of the lower tube half10′ are offset with respect to one another in the transverse direction. The distance between the lugs32in the flow direction of the exhaust gas amounts to approximately 30 mm.

In the case of the embodiment according toFIGS. 4aand4b, the lugs32′ are molded in each case out of the tube half10′ by means of deep drawing and pressing-together. A welding operation, particularly a seal welding, in the area of the lugs32′ is therefore eliminated.FIG. 4aalso shows that the tube half10′ is provided with an outward-directed button-type shaping-out33. These shaped out parts33which, in each case, are arranged in the flow direction between the successive pairs of lugs32′ are used as spacers or spacing elements with respect to the concerned adjacent rectangular tube. Such an arrangement of spacers has advantages particularly in the case of fairly long heat exchangers.

FIG. 5ashows a structural element which is an edged sheet metal part34which forms pairs of lugs35. This structural part34can be fastened on the tube halves10′ in the area of the web connecting the lugs35by means of point welding. This also eliminates seal welding. In a modified embodiment similar toFIGS. 5aand5b, the web of the structural part34connecting the lugs35is provided with lugs which are edged to the opposite side and which are fitted into the slots of the tube half10′ and are welded in and project toward the outside in order to form spacers with respect to the adjacent rectangular tubes10.

FIG. 6illustrates an embodiment of rectangular tubes which are formed of two tube halves36divided in the longitudinal direction in the area of the larger walls. A plate37, which is deformed into S- and-Z-shaped successive sections, is inserted into the two tube halves36. The parts, which in each case extend in parallel to the longer walls of the tube half36, are provided with pairs of lugs38which are arranged and constructed corresponding to the explanations regardingFIGS. 3aand3b. The tube halves36are connected with one another, for example by laser welding or micro TIG welding, in which case the inserted plate37is fixed by means of a weld-through.

During manufacture of the present heat exchanger, the tube halves10′ are first provided with the lugs32,32′,35or38and are then welded together. The thus formed rectangular tubes are arranged in tube bottoms11stamped out in a latticed construction, after which the ends of the rectangular tubes10are welded to the tube bottoms. Subsequently, the two profiled sheet metal shells of the sheet metal jacket12, which are provided with the prepared inlet openings and outlet openings for the cooling medium, are joined to the tube bottoms11and welded to them. Then the flange plates15are mounted and are welded to the sheet metal jacket12. Subsequently, the prepared threaded sleeves19,20are fitted onto the flange plates and are welded to them and are welded by means of the holding webs21,27to the sheet metal jacket12. Then the cover plates28are mounted which are welded to the holding webs27, the sheet metal jacket12, the connection tubes24, the threaded sleeves20and the flange plates15in such a manner that a type of water chamber is formed.