Patent Application
20090013678
This application claims the benefit of German patent application Serial No. DE 102008002746.4 filed Jun. 27, 2008, which is hereby incorporated herein by reference in its entirety.
The present invention relates to a heat exchanger for an exhaust gas train of a motor vehicle, and more specifically to an exhaust gas recirculation system for an internal combustion engine of a motor vehicle, a method for producing an exhaust gas heat exchanger for the recirculation system, and an assembly tool suitable for use within the scope of the manufacturing method.
As a result of the increasingly stringent legal regulations in relation to the exhaust gas emissions of motor vehicles, particularly in relation to the emission of nitrogen oxides, in the area of the internal combustion engine the return of combustion exhaust gases to the inlet side of the internal combustion engine is prior art. The combustion gases themselves do not participate again in the combustion process in the combustion chamber of the internal combustion engine but thus constitute an inert gas which dilutes the mixture of combustion air and fuel in the combustion chamber and provides inner mixing. In this way, it is possible to minimize the occurrence of so-called hot spots during the combustion process which are characterized by locally extremely high combustion temperatures. Such very high combustion temperatures promote the formation of nitrogen oxides and must therefore be avoided at all costs.
Since the efficiency of an internal combustion engine typically depends on the temperature of the combustion air fed to the combustion chamber of the internal combustion engine, the combustion gases from the combustion chamber of the engine cannot be fed back immediately to the intake side. Rather, a significant reduction in the combustion temperature is required. Typical outlet temperatures of the combustion gases from the combustion chamber of the internal combustion engine are in the range of 900° C. or higher whereas the temperature of the combustion air fed to the inlet side of the combustion chamber of the internal combustion engine should not be above 150° C., preferably significantly less than this. For cooling the returned combustion gases, it is known from the prior art to use so-called exhaust return coolers. Various designs are known from the prior art in which the combustion gases to be cooled are passed through exchange tubes with a coolant flowing around the outside, the coolant generally being the cooling water of the motor vehicle. In order to enhance the efficiency it is proposed in the prior art to pass the combustion gases to be cooled through a bundle of exchanger tubes connected in parallel in terms of fluid flow, the coolant generally flowing around the tubes.
Known from DE 10 2005 055 482 A1 is an exhaust gas heat exchanger for an internal combustion engine in which those surfaces coming in contact with the hot combustion gases are executed as corrosion-resistant steel surfaces. The heat exchanger tubes and the housing in which the heat exchanger tubes are located are configured as separate parts which need to be joined together during the production process.
General information of the exhaust gas return technology in internal combustion engines in motor vehicles can be deduced, for example, from DE 1000 119 54 A1.
It would be desirable to produce a heat exchanger for an exhaust train of a motor vehicle that offers advantages in manufacturing costs over the prior art constructions; provide a method for assembling the heat exchanger; and provide an assembly tool suitable for facilitating the assembly of the heat exchanger according to the method.
Compatible and attuned with the present invention, a heat exchanger for an exhaust train of a motor vehicle that offers advantages in manufacturing costs over the prior art constructions; a method for assembling the heat exchanger; and an assembly tool suitable for facilitating the assembly of the heat exchanger according to the method, have surprisingly been discovered.
A heat exchanger according to the invention is provided for the exhaust gas line of a motor vehicle. It comprises at least one separately configured, exhaust-gas-carrying exchanger tube which is located in a separately configured closed housing. This housing for its part has cooling flowing therethrough, which coolant therefore also flows around the outside of the exchanger tube. The coolant can, for example, be the coolant of the internal combustion engine itself, i.e. the exhaust gas heat exchanger can be located in the coolant circuit of the motor vehicle. The inlet and/or the outlet of the at least one exchanger tube are located outside the housing of the heat exchanger, the exchanger tube being guided through a wall of the housing at least one feed-through point in a coolant- and/or exhaust gas-tight manner. The media coolant and exhaust gas can optionally also be exchanged.
According to the invention, a mechanical support structure lying in the interior of the housing is now formed on the outer surface of the exchanger tube and a mechanical retaining structure lying outside the housing is formed at the exterior end of the exchanger tube.
The two support or retaining structures substantially simplify the assembly process required to produce the heat exchanger according to the invention and therefore allow a significant cost saving. They also ensure increased reliability of the coolant- or gas-tight passage of the at least one exchanger tube through the wall of the heat exchanger.
In an embodiment, the mechanical support structure lying in the interior of the housing is configured in the form of one or a plurality of expanded tube sections. Alternatively, it is also possible to attach a separately configured support structure to the outside of the exchanger tube and fix it there by means of suitable mechanical means. As an example, mention is made here of an annular collar which is pushed onto the outside of the exchanger tube and clamped firmly there, fixed or soldered by means of spot welds.
The mechanical retaining structure lying outside the housing at the outer end of the exchanger tube can again advantageously be formed by one or a plurality of expanded tube sections. In particular, the outer end of the exchanger tube can be completely or partially beaded for this purpose to form a collar-like retaining structure. Naturally, it is also possible here to provide a separately configured mechanical retaining structure, for example, in the form of a ring which is pushed onto the outer end of the exchanger tube during assembly of the heat exchanger according to the invention and is mechanically fixed there in a suitable manner.
The separate configuration of housing and exchanger tube in the heat exchanger according to the invention allows the same to be manufactured particularly simply and also makes it possible to use materials for the heat exchanger according to the invention which are in each case adapted to the locally prevailing requirements with regard to corrosion resistance and heat resistance of the materials.
It has proved to be advantageous, for example, if the exchanger tube or tubes are made of a corrosion-resistant and heatproof material such as, for example, stainless steel. Stainless steel also has the advantage of being flexible so that the curvature according to the invention of the flow path in the exchanger tube/in the exchanger tubes can easily be achieved. If less stringent requirements are imposed on the corrosion resistance or on the heat resistance, it can be sufficient to make the exchanger tube/exchanger tubes from aluminum or aluminum alloy. Seamlessly drawn tubes are preferably used.
The housing of the exhaust gas heat exchanger according to the invention can naturally also consist of stainless steel, for example, a seamlessly drawn stainless steel tube with an inserted bottom piece. Particular advantages are achieved if the housing is configured as a cast part, i.e. in particular consists of a castable material such as, for example, aluminum, magnesium, gray cast iron or a plastic having a sufficient temperature resistance. However, since the housing of the exhaust gas heat exchanger according to the invention does not come in contact with the corrosive combustion exhaust gases and is exposed to temperatures lying at typical coolant temperatures such as in the range below 150°, the aforesaid significantly more favorable materials can be avoided. In particular, the housing can be produced in a casting process, for example, by means of plastic or metal, injection molding. In addition to the cost advantages already mentioned and the fact that a cast housing is easier to manufacture, substantial savings in weight can also be reduced with cast housings compared with stainless steel housings, which is another advantage of the exhaust gas heat exchanger according to the invention since an undesirable side effect of the increasing complexity of motor vehicles is their continuous increase in weight which goes against the efforts of motor vehicle manufacturers to reduce the consumption and emissions of motor vehicles.
In a particularly preferred embodiment, the heat exchanger comprises a housing configured as at least two-part. In particular, the housing can form a housing cover and a jacket portion, wherein the jacket portion can be configured as pot-shaped and can be tightly closed by the housing cover.
In this preferred embodiment, the exchanger tube is then guided in a gas- and fluid-tight manner through at least one of the two housing parts, for example, through the housing cover. In this way, the inlet and the outlet of the exchanger tube are therefore located outside the housing. In particular, the exchanger tube can be mechanically firmly connected to this housing part at the points at which it is guided through the housing part so that the exchanger tube is completely mechanically supported on this housing part.
The two housing sections, in particular therefore the housing cover and the jacket portion are preferably configured as separate parts which are connected to one another by means of mechanical retaining means such as, for example, screws or rivets.
Since the housing cover or that housing section through which the at least one exchanger tube is guided is in thermal contact with the exchanger tube, further advantages are achieved if this housing section, i.e. for example, the housing cover, is made of a corrosion-resistant and heat-proof material such as stainless steel. With certain restrictions, the use of aluminum or aluminum alloy or other metallic materials having suitable heat resistance is also suitable here provided that this can be connected in a suitable gas- and liquid-tight manner to the exchanger tube guided therethrough, for example, by means of soldering, welding or possibly also adhesive bonding.
Particular advantages are obtained in this connection if the housing section in question, i.e. in particular the housing cover and the at least one exchanger tube are made of the same material, i.e. for example stainless steel.
Further advantages are obtained if the feed-through points, i.e. those points at which the at least one exchanger tube is guided through the wall of the housing on the inlet side and on the outlet side, are substantially arranged in a common plane E. The inlet and the outlet of the exchanger tube can be substantially arranged in a common plane E′ which in particular can coincide with the aforesaid common plane of the feed-through points. One of the planes E or E′ can form an interface for a connection of a heat exchanger to the exhaust gas system of the motor vehicle whereby the heat exchanger according to the invention can be assembled particularly easily.
This advantages can be increased still further by arranging the coolant inlet and the coolant outlet for the coolant flowing through the housing of the heat exchanger according to the invention likewise in the plane E of the feed-through points of the exchanger tube or in the plane E′ of the inlet and the outlet of the exchanger tube. In a particularly preferred embodiment, the planes E and E′ coincide so that both the feed-through points and also the inlet and outlet of the exchanger tube and also the coolant inlet and coolant outlet are arranged substantially in one plane. This common plane can then advantageously form an interface for a connection of the heat exchanger both to the exhaust gas system of the motor vehicle and also to the coolant system of the motor vehicle.
Further advantages are obtained if the exchanger tubes of the heat exchanger according to the invention are substantially one-piece between their inlet and their outlet, but are at least one-piece between the aforesaid feed-through points. In particular, the at least one exchanger tube can be substantially semicircular or bent in a U shape between its inlet and its outlet or its feed-through points.
In a preferred exemplary embodiment, instead of a single exchanger tube in the heat exchanger according to the invention, there is provided a bundle of exchanger tubes which are connected fluid-dynamically in parallel. In particular, this bundle of exchanger tubes should be configured such that the flow paths formed in the individual exchanger tubes between their respective inlets and outlets have no contact with the flow paths in the adjoining exchanger tubes. This avoids the exhaust gas stream to be cooled having to pass many times through cross-sectional constrictions on its passage through the exhaust gas heat exchanger according to the invention. On the one hand, this results in a significantly reduced flow resistance of the heat exchanger according to the invention and on the other hand, it has been found in practical operation that any constriction in the flow path inside an exhaust gas heat exchanger forms a location at which condensate contained in the returned combustion exhaust gas deposits, which in the long term can result in partial or complete blockage of the heat exchanger and therefore failure of the entire exhaust gas return system of the motor vehicle.
If a bundle of exchanger tubes is used, it has proved to be particularly optimal when using water as coolant if the minimum distance d between the outer surfaces of the adjacently arranged exchanger tubes is in the range between 0.5 mm and 5 mm. Particularly preferred here is a gap width between 1 and 2 mm which again in particular with reference to water as coolant, constitutes an optimum in relation for flow resistance for the coolant on the one hand and an optimization of the surface of the exchanger tubes around which flow takes place in relation to the volume through which coolant flows on the other hand.
With regard to the dimensions of the exchanger tubes in a the heat exchanger according to the invention, it has proved to be favorable if the at least one exchanger tube has an outside diameter D between 1 and 15 mm. Particularly preferred in this case is the range between 6 and 12 mm for which the ratio between the established pressure loss or flow resistance for the return combustion exhaust gas on the one hand and the thermal resistance of the exhaust gas heat exchanger according to the invention on the basis of the tube cross-section to the inner surface of the heat exchanger tubes on the other hand has proved to be optimal.
If a bundle of exchanger tubes is used, both the mid points of the inlets and of the outlets of the exchanger tubes lie on the mid points of an orthogonal or hexagonal grid. Both the inlets and the outlets are preferably arranged on grid points of equivalent grids. Alternatively or additionally, the feed-through points at which the individual exchanger tubes are guided through the wall of the housing of the heat exchanger on the inlet side and on the outlet side could be arranged on grid points of comparable grids. Such an arrangement of the inlets or outlets of the exchanger tubes or of their feed-through points through the wall of the exchanger housing again allows particularly efficient usage of the space available inside the exchange housing.
In a particularly preferred further development of the heat exchanger according to the invention comprising a bundle of exchanger tubes, the exchanger tubes are arranged so that they cross at least in pairs. In this way, particularly efficient use of space inside the housing of the heat exchanger can be ensured.
In a simple first embodiment, the at least one exchanger tube can be configured as a smooth-walled tube where smooth-walled relates both to its inner and to its outer surface. In an improved embodiment, the at least one exchanger tube is configured as a twisted tube i.e. a spiral structure is formed on the inner surface of the exchanger tube, which sets the through-flowing gas stream into vortex motion as it flows through the (bent) exchanger tube.
In particular, such a spiral structure can be brought about by incorporating a spiral indentation structure in the wall of an otherwise smooth-walled tube e.g. made of stainless steel.
A method according to the invention is provided for mounting a separately configured e.g. exhaust-gas-carrying exchanger tube of a heat exchanger for the exhaust gas line of a motor vehicle. In the heat exchanger, the exchanger tube is located in a separately configured closed housing which has a coolant (or alternatively also exhaust gas) flowing therethrough. In this case, the medium flowing through the housing flows around the outside of the exchanger tube. The inlet and/or the outlet of the exchanger tube are located outside the housing, and the exchanger tube is guided through a wall of the housing at a feed-through point in a coolant- and/or exhaust gas-tight manner. The exchanger tube itself can either have exhaust gas or coolant flowing therethrough. The method according to the invention is characterized by the following process steps:
In a particularly preferred embodiment of the method according to the invention, steps b) and c) are carried out substantially at the same time, for example, using a suitable assembly tool.
In an alternative but likewise advantageous embodiment of the method according to the invention, step a) is carried out after step b) and before step c).
In another advantageous embodiment of the method according to the invention, in order to form a mechanical support structure lying in the interior of the housing on the outer surface of the exchanger tube, this exchanger tube itself is expanded at least in sections, for example, using a suitable assembly tool designed as a pipe-expanding tool. Furthermore, the mechanical retaining structure (28) lying outside the housing at the outer end of the exchanger tube can likewise advantageously be produced by means of expansion of the exchanger tube, at least in sections. In particular, the outer (short) end of the exchanger tube can be beaded for this purpose.
A pipe expanding tool can advantageously be inserted into the inside of the exchanger tube to carry out steps b) and/or c).
The coolant- and/or gas-tight mechanical connection between the housing and the exchanger tube can advantageously be made in a further process step by means of one of the following methods:
Naturally, all other joining methods known from the prior art as suitable for the task, in particular the materials used and the temperature range in question can be used in principle.
With regard to the production of the coolant- and/or gas-tight mechanical connection between the housing and the exchanger tube by means of crimping, it should be noted at this point that when forming the mechanical support structure and the mechanical retaining structure by at least partial expansion of the exchanger tube, this can be executed so that a coolant- and/or gas-tight connection between the housing and the exchanger tube is obtained immediately without executing further processes. This should be regarded as a special case of crimping.
With regard to the soldering of exchanger tube and housing, it has proved to be advantageous if the outer surface of the exchanger tube is coated with a suitable solder, at least in sections, before carrying out the soldering. Likewise it has provided advantageous if the inner and/or outer surface of the housing is additionally or alternatively coated with solder, at least in sections, before carrying out the soldering. In the procedure described hereinbefore, for example, automated fitting of the housing/housing cover with the exchanger tubes can be effected and these fixed mechanically on the housing forming the support or retaining structures. The exchanger tubes and the housing/housing cover thus combined to form a mechanical unit can then be passed through a soldering furnace, wherein no additional measures are required to fix the exchanger tube or tubes mechanically on the housing/housing cover during the soldering process.
An assembly tool to be used advantageously in the method according to the invention has the following features:
In this case, for example, the cross-section of the mandrel to be inserted into the exchanger tube can be enlarged in sections. In particular, this cross-sectional enlargement can be based on the expansion of a flexible body, for example, consisting of a synthetic rubber.
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:
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.
At the front, the jacket portion 59 forms a flange 59 for connection to a housing cover 60. In the exemplary embodiment shown, the housing cover 60 consists of a stamped stainless steel plate having a thickness of a few millimeters, preferably about 2 mm. The jacket portion 50 is connected in a liquid- and gas-tight manner to the housing portion 60 with an interposed seal 52 which is configured as a metal thickness seal in the exemplary embodiment shown. In this case, the housing cover 60 is screwed to the flange 59 of the jacket portion 50 by means of screws 54, for which the jacket portion 50 has a plurality of large threaded holes 55. At corresponding positions, the housing cover 60 has large-diameter through-holes 65 through which suitably-sized screws 54 can be guided and inserted into the threaded holes 55 so that the housing cover 60 can be screwed to the jacket portion 50.
The jacket portion 50 forms an inner space 42 which is provided to receive a bundle of U-shaped bent exchanger tubes 20. In this case, the exchanger tubes 20 have identical tube dimensions such as inside and outside diameter, but the opening width W of the U-shaped profile varies. However, the shaping of the inner space 42 and therefore also of the jacket portion 50 as a whole is adapted to the shaping of the bundle of exchanger tubes 20 so that the usage of the inner space 42 by the bundle of exchanger tubes 20 is as efficient as possible.
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 guided into corresponding holes in the housing cover 60 which form feed-through points 66, 68 for the inlets or outlets of the exchanger tubes 20. At the same time, the inlets and outlets 22, 24 of the exchanger tubes 20 are guided through the feed-through points 66, 68 formed in the housing cover 60, and the exchanger tubes 20 are connected in a gas- and liquid-tight manner to the housing cover 60 at the feed-through points 66, 68, for example, by means of soldering or welding. This provides mechanical support of the exchanger tubes 20 on the housing cover 60.
In an embodiment, the exchanger tubes 20 consist of thin-walled stainless steel tubes, the exchanger tubes 20 being provided with an embossed structure, so that a spiral structure 26 rises from the inner surface of the exchanger tubes 20. The bundle of exchanger tubes 20 is arranged so that all the inlets 22 and all the outlets 24 are each arranged in a cohesive group so that the heat exchanger 1 according to the invention can easily be connected to the exhaust gas system of the motor vehicle. For this purpose the front side of the housing cover 60 forms an assembly interface S which, as a result of the planar design of the housing cover 60, is configured as substantially flange-like. For mounting the heat exchanger 1 on the motor vehicle, further threaded holes 53 are formed in the jacket portion 50 which have a reduced inside diameter compared with the threaded holes 55. Corresponding through holes 63 are formed in the metal bead seal 52 and in the housing cover 60. By this means, the heat exchanger 1 can be connected to the exhaust gas and coolant system of the motor vehicle by means of a plurality of screws not shown in
In addition to the inner space 42 not occupied by the bundle of exchanger tubes 20, the jacket portion 50 forms an inlet channel 56 and an outlet channel 58 for a coolant which, for example, can comprise cooling fluid of the motor vehicle. The inlet channel 56 and outlet channel 58 are arranged in this case so that when the heat exchanger 1 is operated as prescribed, a flow path extending from top to bottom (in
The inlet channel 56 formed in the jacket portion 50 and the outlet channel 58 likewise end in the flange 59 formed by the jacket portion 50, wherein webs 57 are formed at the ends of the channels 56 and 58, which form a mechanical support for the metal bead seal 52 resting on the flange 59. This likewise forms openings for the coolant flowing through the heat exchanger 1 which correspond to the coolant inlet 62 and coolant outlet 64 formed in the housing cover 60. In the assembled heat exchanger 1, coolant can thus be thus be supplied via the front side of the housing cover 60 via the coolant inlet 62 and removed via the coolant outlet 64 and the combustion exhaust gas to be cooled can be supplied via the inlets 22 of the exchanger tubes 20 and removed via the outlets 24. In the design shown, this is possible via a single common assembly interface S.
This is particularly clear from the diagram according to
The exchanger tube 20 has an outside diameter D which is typically in the range between 1 and 15 cm, preferably in a range between 6 and 12 mm, since this has proved to be particularly suitable for use of the heat exchanger as prescribed as an exhaust gas heat exchanger for a motor vehicle. It can be seen from
The outside end of the exchanger tube 20 is completely peripherally beaded to form the retaining structure 28 so that a mechanical support of the exchanger tube 20 on the housing cover 60 is obtained overall from the combination of the support structure 27 and the beaded end 28. This results in a substantial simplification in the manufacture of the heat exchanger 1 according to the invention since the exchanger tubes 20 are already mechanically pre-fixed in the housing cover 60. In this way, an additional fixing of the exchanger tubes 20 on the housing cover 60, for example, by means of (laser) spot welds during a subsequent soldering or welding of the exchanger tube ends to the housing cover 60 can be dispensed with.
The support and retaining structures 27, 28 shown in
The pipe expanding tool 30 comprises a mandrel 31 whose outside diameter is adapted to the inside diameter of the exchanger tube 20, so that the mandrel 31 can be inserted into the end of the exchanger tube 20. The mandrel 31 is formed, in sections, of a flexible incompressible material such as synthetic rubber. These flexible elements are designated by the reference numeral 32 in
A more efficient utilization of space is obtained in the arrangement of the inlets 22 or outlets 24 according to
Finally,
In order to form the gas- and liquid-tight passage of the exchanger tubes 20 through the housing cover 60, the exchanger tubes 20 are then soldered to the housing cover 60 in a gas- and liquid-tight manner by means of the soldering process which has already been described previously. At least in the area of a housing cover 60 the exchanger tubes 20 are fixed for the soldering process on the housing cover by formation of the additional retaining structure 28 at the outer end of the exchanger tubes 20. This can again also be achieved by beading the outer end of the exchanger tube.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| DE102007032331.1 | Jul 2007 | DE | national |
| DE102008002746.4 | Jun 2008 | DE | national |
