Heat exchanger

Abstract

Heat exchanger (1) for the exhaust system of a motor vehicle with a separately formed exhaust gas-carrying heat exchanger tube (20) arranged in a separately formed closed housing through which a coolant flows, which flows around the outside of the heat exchanger tube (20), wherein the housing forms at least a housing cover (60) and a jacket part (50), wherein the jacket part (50) is tightly closed by the housing cover (60), and both ends of the heat exchanger tube (20) are guided through the housing cover (60) in a gas- and liquid-tight manner, so that the inlet (22) and the outlet (24) of the heat exchanger tube (20) are arranged outside the housing, and the heat exchanger tube (20) is substantially U-shaped or semicircularly bent between the points where it passes through the housing cover (60), and the heat exchanger tube (20) is designed as a swirl tube, wherein a plurality of heat exchanger tubes (20) form a bundle, characterized bythat a guide plate (36) is arranged within the bundle of heat exchanger tubes (20), which is mechanically firmly connected to the adjacent heat exchanger tubes (20) at its lateral wall and its bent tip.

Description

[0001] The subject of the present invention is a heat exchanger for the exhaust system of a motor vehicle, in particular for an exhaust gas recirculation system for an internal combustion engine of a motor vehicle, having the features of the preamble of the main claim.

[0002] Due to the ever-increasing legal regulations regarding motor vehicle exhaust emissions, particularly with regard to nitrogen oxide emissions, the recirculation of combustion exhaust gases to the intake side of the internal combustion engine is state of the art in the field of internal combustion engines. The combustion gases themselves do not participate in the combustion process in the combustion chamber of the internal combustion engine and thus represent an inert gas that dilutes the mixture of combustion air and fuel in the combustion chamber and ensures more thorough mixing. This makes it possible to minimize the occurrence of so-called "hot spots" during the combustion process, which are characterized by extremely high local combustion temperatures. Such very high combustion temperatures promote the formation of nitrogen oxides and must therefore be avoided at all costs.

[0003] Since the efficiency of an internal combustion engine typically depends on the temperature of the combustion air supplied to the combustion chamber, the combustion gases cannot be fed directly back to the intake side after they exit the combustion chamber. Instead, a significant reduction in the combustion gas temperature is required. Typical outlet temperatures of the combustion gases from the combustion chamber of an internal combustion engine are in the range of 900°C and above. The temperature of the combustion air supplied to the inlet side of the combustion chamber of the internal combustion engine, on the other hand, should not exceed 150°C, and preferably be significantly lower. To cool the recirculated combustion gases, the use of so-called exhaust gas recirculation coolers is known from the prior art.A wide variety of designs are known from the prior art, in which the combustion gases to be cooled are generally guided through exchanger tubes, around which a coolant flows on the outside. The coolant is usually the vehicle's cooling water. To increase efficiency, the prior art proposes guiding the combustion gases to be cooled through a bundle of exchanger tubes arranged in parallel, each of which is surrounded by the coolant.

[0004] DE 10 2004 019 554 A1 discloses an exhaust gas recirculation system for an internal combustion engine, which comprises an exhaust gas heat exchanger designed as a two-part cast part. Since the very hot combustion gases are reactive due to the fuel never being fully burned, the problem arises that it is technically difficult, if not impossible, to design the surfaces of a metallic cast part as inert surfaces comparable to a stainless steel surface.

[0005] DE 10 2005 055 482 A1 discloses an exhaust gas heat exchanger for an internal combustion engine that avoids the aforementioned problems by designing the surfaces that come into contact with the hot combustion gases as corrosion-resistant steel surfaces. The heat exchanger tubes and the housing in which the heat exchanger tubes are arranged are designed as separate parts that are joined together during the manufacturing process.

[0006] In the exhaust gas heat exchanger known from DE 10 2006 009 948 A1, the channels carrying the hot gas and the housing, in which the coolant flows around the exhaust gas channels, are integrally formed in the form of a plate heat exchanger. Both the flow paths for the hot combustion gases and the flow paths for the coolant are only formed when individual, for example, deep-drawn, plates are joined together to form a plate heat exchanger. A similar concept is also pursued in DE 10 2006 049 106 A1.

[0007] General information on exhaust gas recirculation technology in internal combustion engines in motor vehicles can be found, for example, in DE 100 119 54 A1.

[0008] DE 10 2005 054 731 A1 discloses a U-shaped, counterflow aluminum exhaust heat exchanger for automotive engines. The heat exchanger comprises a die-cast housing shell and an inserted flange plate with U-shaped, extruded flat tubes fitted and secured to it.

[0009] From US 2,303,613 A, a heat exchanger with a plurality of U-shaped exchanger tubes is known, which are arranged in a common jacket through which coolant flows and can cross each other in pairs.

[0010] US Pat. No. 1,355,980 A also discloses a heat exchanger with a plurality of U-shaped exchanger tubes arranged in a common shell through which coolant flows. The exchanger tubes have a round cross-section at their end regions and are flattened in the region between them.

[0011] Finally, JP H09-229,579 A discloses a heat exchanger with a plurality of U-shaped exchanger tubes designed as swirl tubes.

[0012] The object of the invention is to provide a heat exchanger for the exhaust system of a motor vehicle which has advantages in terms of weight and manufacturing costs compared to the designs previously known from the prior art.

[0013] This problem is solved by an exhaust gas heat exchanger for the exhaust system of a motor vehicle having the features of the main claim.

[0014] A heat exchanger according to the invention is intended for use in the exhaust system of a motor vehicle, here in particular for cooling the exhaust-side combustion exhaust gases recirculated to the inlet side of the combustion chambers of the internal combustion engine. The heat exchanger has at least one separately designed exhaust-gas-carrying exchanger tube, which is arranged in a separately designed closed housing. A coolant flows through this housing, which can be, for example, the coolant from the coolant circuit of the internal combustion engine of the motor vehicle. The coolant flowing through the housing flows around the outside of the at least one exchanger tube, absorbs the combustion heat carried by the recirculated combustion exhaust gas, and dissipates it via the coolant circuit of the motor vehicle.

[0015] According to the invention, the heat exchanger housing is divided into at least two housing sections, namely a housing cover and a shell part. The shell part is tightly sealed by the housing cover. According to the invention, both ends of the at least one exchanger tube are passed through a common housing section of the heat exchanger housing in a gas- and liquid-tight manner, whereby this housing section is referred to as the cover part in the context of the present invention. As a rule, the housing section referred to as the shell part then encloses the exchanger tube mechanically secured to the cover part, forming the heat exchanger housing.Alternatively, it is also possible for the cover part itself to virtually completely enclose the exchanger tube mechanically supported by it, and for the housing of the heat exchanger according to the invention to be closed by attaching a second housing section referred to as the shell part, even if the housing section, again referred to as the "shell part," in this embodiment practically does not enclose the exchanger tube. Mixed forms of housing cover and shell part are of course also possible, in which both the housing cover and the shell part partially enclose the at least one exchanger tube.

[0016] By forming the exchanger tube and housing of the heat exchanger according to the invention separately, these fundamental components for the heat exchanger according to the invention can be made of different materials. Furthermore, by dividing the housing into two housing sections, with the two ends of the at least one exchanger tube passing through only one housing section, the material of this housing section can be specifically adapted to the thermal, mechanical, and / or corrosion-related requirements of the intended use. Particular advantages arise when the at least one exchanger tube is made of a corrosion-resistant and heat-resistant material such as stainless steel or aluminum.The use of stainless steel also offers the advantage of increased flexibility, which is a significant advantage, for example, when implementing a winding flow path within the exchanger tube. If less stringent requirements are placed on corrosion resistance or heat resistance, a design of at least one exchanger tube made of aluminum or an aluminum alloy may be sufficient.

[0017] The housing cover is advantageously made from the same material as at least one exchanger tube, as this ensures good mechanical connection between both parts and reduced susceptibility to corrosion. If both parts, i.e. housing cover and exchanger tube, are made from stainless steel, excellent corrosion resistance with very high thermal resilience is ensured. Furthermore, the poorer thermal conductivity of stainless steel minimizes the transfer of waste heat from the very hot combustion exhaust gases via the housing cover to the shell part. With certain restrictions, the use of aluminum or an aluminum alloy or other metallic materials with suitable heat resistance is also suitable here, provided that this can be connected to the exchanger tube passing through in a suitable gas- and liquid-tight manner, for example by soldering, welding or if necessary.also gluing.

[0018] The shell part of the housing of the exhaust gas heat exchanger according to the invention can of course also be made of stainless steel, for example from a seamlessly drawn stainless steel tube with an inserted base piece. However, the division of the heat exchanger housing makes it possible to form the shell part as a cast part, which results in particular advantages. Thus, the shell part of the housing can be made of a castable material such as aluminum, an aluminum alloy, magnesium or magnesium alloy, gray cast iron, or a plastic that has sufficient temperature resistance. Since the shell part of the housing of the exhaust gas heat exchanger according to the invention does not come into contact with the corrosive combustion gases, and the temperatures are limited to typical coolant temperatures in the range below 150°C, the significantly more favorable materials mentioned above can be used instead.In particular, the shell part of the housing can be manufactured by casting, for example by plastic or metal injection molding or other inexpensive processes such as deep drawing. In addition to the already mentioned cost advantages and the easier manufacturing of a cast or drawn shell part of the housing, cast housing parts can also achieve significant weight savings compared to stainless steel housings, which represents a further advantage of the exhaust gas heat exchanger according to the invention. An undesirable side effect of the increasing complexity of motor vehicles is their constant increase in weight, which runs counter to the efforts of motor vehicle manufacturers to reduce fuel consumption and emissions.

[0019] Particular advantages arise if a seal is inserted between the casing part and the housing cover. This can in particular be a seal made of a metallic material such as a metal bead seal or an elastic seal (e.g. elastomer seal). In this context it is particularly advantageous if the housing cover and the casing part are designed as separate parts which are connected to one another by means of mechanical holding means. Screws or rivets, for example, can be used as such holding means. Of course, any other mechanical holding means are also conceivable, provided they are known from the prior art and are suitable for at least a one-time connection between the housing cover and the casing part. A connection without any tools, such as flanging or similar, can also be advantageous in this context.

[0020] In a particularly preferred embodiment of the heat exchanger according to the invention, its housing cover forms an interface for connecting the heat exchanger to the exhaust system of the motor vehicle. This significantly simplifies the installation of the heat exchanger according to the invention in the motor vehicle.

[0021] The exchanger tube of the heat exchanger according to the invention is preferably constructed in one piece, at least between the points where it passes through the housing cover of the heat exchanger housing. It can be bent, in particular, in a U-shape or semicircular shape. In this way, corrosion phenomena at transition points between tube sections can be prevented. Furthermore, with this preferred embodiment, only a single flow-mechanical constriction occurs when flowing through the exhaust gas heat exchanger, thereby minimizing the pressure drop in the exhaust gas flowing through the heat exchanger.

[0022] In a particularly preferred embodiment, the flow path extending within the exchanger tube for the combustion exhaust gas to be cooled runs as a winding flow path, at least within the housing of the heat exchanger. In particular, this flow path can enclose a rotation angle α of at least 45° within the housing, but preferably a rotation angle α between 135 and 225°. Particularly preferably, it encloses an angle of 180°, i.e., the cooled combustion exhaust gas exiting the heat exchanger according to the invention leaves the heat exchanger in the direction opposite to the inlet direction.

[0023] Due to the curved design of the flow path of the combustion exhaust gas to be cooled, space utilization is significantly improved compared to prior art exhaust gas heat exchangers with typically straight-line exchanger tubes. The separate design of the housing and exchanger tubes of the heat exchanger according to the invention allows for particularly simple production and also enables the use of materials for the heat exchanger according to the invention that are adapted to the locally prevailing requirements regarding corrosion resistance and heat resistance.

[0024] In a preferred embodiment, the heat exchanger according to the invention, instead of a single exchanger tube, is provided with a bundle of exchanger tubes connected in parallel for fluidic purposes. In particular, this bundle of exchanger tubes should be designed 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 adjacent exchanger tubes. This prevents the exhaust gas stream to be cooled from having to pass through cross-sectional constrictions multiple times as it passes 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 every constriction in the flow path within an exhaust gas heat exchanger forms a location at which condensate and particles contained in the recirculated combustion exhaust gas are deposited, which in the long term can lead to a partial or complete blockage of the heat exchanger and thus to the failure of the entire exhaust gas recirculation system of the motor vehicle.

[0025] If a bundle of exchanger tubes is used, it has proven optimal, especially when using water as the coolant, for the minimum distance between the outer surfaces of the adjacent exchanger tubes to be in the range between 0.5 mm and 5 mm. A gap width of between 1 mm and 2 mm is particularly preferred. This gap width represents an optimum, particularly with regard to water as the coolant, both in terms of the flow resistance for the coolant and in terms of optimizing the surface area of ​​the exchanger tubes in relation to the volume through which the coolant flows.

[0026] If a bundle of exchanger tubes is used, it has proven to be optimal in terms of space utilization if both the center points of the inlets and the center points of the outlets of the exchanger tubes or alternatively the support points, i.e. the points at which the exchanger tubes penetrate the wall of the heat exchanger housing, lie on the center points of an orthogonal or hexagonal grid. Preferably, both the inlets and the outlets or the support points are arranged on grid points of equivalent grids. Alternatively or additionally, the feed-through points at which the individual exchanger tubes are led through the wall of the heat exchanger housing on the inlet and outlet sides could also be arranged on grid points of comparable grids. Such an arrangement of the inlets and outlets of the exchanger tubes orThe insertion points through the wall of the exchanger housing allow for particularly efficient use of the available space inside the exchanger housing. In particular, a hexagonal arrangement of the exchanger tubes results in a particularly intensive filling of the space inside the heat exchanger housing with the exchanger tubes, thus effectively minimizing space.

[0027] The use of space inside the heat exchanger housing can be further optimized, especially with a U-shaped configuration of the exchanger tubes, if the exchanger tubes are arranged in such a way that they cross each other at least in pairs.

[0028] The at least one exchanger tube, but in a preferred embodiment also the majority of the exchanger tubes of the bundle, can be designed as a smooth-walled tube in a simply designed embodiment. Advantages with regard to the thermal efficiency of the heat exchanger according to the invention arise, however, if the at least one exchanger tube, or else the majority of the exchanger tubes, are designed as a swirl tube, i.e. as a tube that is designed such that the hot exhaust gas flow guided within its interior is subjected to intensive swirling. For this purpose, for example, at least the inner surface of the exchanger tube(s) can be equipped with a spiral structure that imparts a swirling motion to the exhaust gas flow flowing through it.

[0029] In particular, such a spiral structure can also be created by introducing a spiral depression structure into the wall of an otherwise smooth-walled tube, e.g. made of stainless steel. A spiral structure on the inner wall of the exchanger tube can be created easily by spirally expanding or deepening a preferably thin-walled exchanger tube, which can be made of stainless steel, for example. The coil spacing DS of such a spiral structure is advantageously between 1 mm and 15 mm, preferably between 3 mm and 8 mm, for the given application and when water is used as the coolant. The height or depth of the spiral structure is again between 1% and 20% of the outer diameter D of the exchanger tube, but preferably between 2% and 16%, for the given application.The outer diameter D of the exchanger tube, again depending on the specific application, is preferably between 1 mm and 15 mm; in particular, the range between 6 mm and 12 mm has proven particularly advantageous. For the preferred range, the ratio between the pressure loss or flow resistance for the recirculated combustion exhaust gas, on the one hand, and the thermal efficiency of the exhaust gas heat exchanger according to the invention, due to the ratio of the tube cross-section to the inner surface of the exchanger tubes, on the other, has proven to be optimal.

[0030] A particularly effective use of space inside the heat exchanger housing is achieved when the exchanger tube is bent essentially in a U-shape or semicircle between the points where it passes through the housing wall. Combined with the design of the exchanger tube as a swirl tube, this results in particularly intensive swirling of the hot exhaust gas flow through the exchanger tube, resulting in particularly effective heat transfer to the wall of the exchanger tube and thus to a transfer into the coolant.

[0031] As already mentioned above, in a preferred embodiment, the at least one exchanger tube, but preferably the majority of the provided exchanger tubes, are mechanically firmly connected to the housing cover at the location of the respective passage through the housing cover. In this way, the at least one exchanger tube / the majority of exchanger tubes are mechanically supported on the housing cover and form an easy-to-handle assembly unit that can be mechanically connected to the shell part of the exchanger housing in the simplest manner during final assembly of the heat exchanger according to the invention.

[0032] Further advantages arise if the feedthrough points, i.e. those points through which the at least one exchanger tube is passed through the heat exchanger housing on the inlet side and outlet side, are arranged substantially in a common plane. The inlet and outlet of the exchanger tube can also be arranged substantially in a common plane, which can in particular coincide with the aforementioned common plane of the feedthrough points. One of the planes can form an interface for connecting a heat exchanger to the exhaust system of the motor vehicle, whereby particularly simple installation of the heat exchanger according to the invention on the coolant circuit or exhaust system of the motor vehicle can be achieved.

[0033] These advantages can be further enhanced if the coolant inlet and the coolant outlet for the coolant flowing through the housing of the heat exchanger according to the invention are also arranged in the plane of the feedthrough points of the exchanger tube or in the plane of the inlet and outlet of the exchanger tube. In a particularly preferred embodiment, the planes coincide, so that both the feedthrough points and the inlet and outlet of the exchanger tube as well as the coolant inlet and coolant outlet are arranged essentially in one plane. This common plane can then advantageously form an interface for connecting the heat exchanger to both the exhaust system of the motor vehicle and the coolant system of the motor vehicle. Preferably, at least the coolant inlet and / or the coolant outlet are formed in the housing cover of the heat exchanger housing.In this way, the mounting interface can be formed on the heat exchanger in the simplest way.

[0034] Further advantages arise when the exchanger tubes of the heat exchanger according to the invention are essentially one-piece between their inlet and outlet, but at least between the aforementioned feedthrough points. In particular, the at least one exchanger tube, which passes through the wall of the housing between its inlet and outlet or its feedthrough points, can be bent in a substantially semicircular or U-shaped manner.

[0035] Finally, it is pointed out that in the heat exchangers according to the invention the media can be exchanged, ie the exchanger tube can also be flowed through by the cooling medium and the housing interior surrounding the exchanger tube can also be flowed through by the media flow to be cooled, e.g. the exhaust gas flow to be cooled.

[0036] A heat exchanger according to the invention is also suitable for use as a charge air cooler in a motor vehicle with an internal combustion engine, in which the combustion air is compressed to above-atmospheric pressure via an upstream compressor, such as a turbocharger or a compressor. It is particularly suitable for use as a charge air cooler in conjunction with a low-pressure exhaust gas recirculation system.

[0037] Further advantages and features of the heat exchanger according to the invention emerge from the subclaims and the exemplary embodiments discussed below, which are explained in more detail with reference to the drawings. In these: Fig. 1: an exploded view of a first embodiment of an exhaust gas heat exchanger according to the invention, Fig. 2: a plan view of the mounting interface of an exhaust gas heat exchanger according to a second embodiment, Fig. 3: a plan view of a bundle of exchanger tubes of an exhaust gas heat exchanger according to a third embodiment, Fig. 4: a schematic representation of an exchanger tube of the heat exchanger according to Fig. 1, Fig. 5: a section through the Fig. 4 shown exchanger tube, Fig. 6: a schematic representation of an exchanger tube forming a winding flow path, illustrating the circulation angle α, Fig. 7: a plan view of the interface formed by a housing cover, in which the inlet and outlet openings are arranged on grid positions of an orthogonal grid, Fig. 8: a plan view of the interface formed by a housing cover, in which the inlet and outlet openings are arranged on grid positions of a hexagonal grid, Fig. 9: a section through an inlet / outlet opening of an exchanger tube in the area of ​​a housing cover, and Fig. 10 a - 10 g: a selection of swirl tubes suitable for use in a heat exchanger according to the invention.

[0038] Fig. 1 shows an exploded view of an exhaust gas heat exchanger 1 according to the invention in accordance with a first exemplary embodiment. The heat exchanger 1 comprises a housing which consists of a shell part 50 which is closed by means of a housing cover 60. The shell part 50 is designed as a cast part and can in particular consist of die-cast aluminum. Alternatively, the shell part 50 in the exemplary embodiment shown can be manufactured from any material which, on the one hand, can be processed using a casting process and, on the other hand, has sufficient thermal stability. However, since the shell part 50 of the heat exchanger 1 according to the invention only comes into contact with the coolant, which generally originates from the coolant circuit of the motor vehicle, temperature resistance up to 150° C is sufficient for most applications. Magnesium and / orMagnesium alloys, grey cast iron or even heat-resistant and injection-moldable plastics have proven to be effective.

[0039] On the front side, the casing part 50 forms a flange 59 for connection to a housing cover 60. In the illustrated embodiment, the housing cover 60 consists of a stamped stainless steel plate with a thickness of a few millimeters, preferably approximately 1 - 2 mm. The casing part 50 is connected to the housing cover 60 in a liquid- and gas-tight manner with the interposition of a seal 52, which in the illustrated embodiment is designed as a metal thickness seal. The housing cover 60 is screwed to the flange 59 of the casing part 50 using screws 54. For this purpose, the casing part 50 forms a plurality of large threaded holes 55. The housing cover 60 has through-holes 65 with a large diameter at the corresponding positions, through which appropriately dimensioned screws 54 are passed and inserted into the large threaded holes 55 so that the housing cover 60 can be screwed to the casing part 50.

[0040] The casing part 50 forms an interior space 42, which is intended to accommodate a bundle of U-shaped exchanger tubes 20. The exchanger tubes 20 are identical in terms of their tube dimensions, such as inner and outer diameters, but the opening width W varies (cf. Fig. 4) of the U-shaped profile. The shape of the interior space 42 and thus also of the shell part 50 is adapted overall to the shape of the bundle of exchanger tubes 20, so that the most effective use of space in the interior space 42 is achieved by the bundle of exchanger tubes 20.

[0041] The exchanger tubes 20 each form an inlet 22 and an outlet 24 at their respective ends. The ends of the exchanger tubes 20 are guided through corresponding bores in the housing cover 60, which form feedthrough points 66, 68 for the inlets 22 and the outlets 24 of the exchanger tubes 20, respectively. The inlets and outlets 22, 24 of the exchanger tubes 20 are guided through the bores formed in the housing cover 60. The exchanger tubes 20 are connected to the housing cover 60 at the feedthrough points 66, 68 in a fluid-tight manner, for example by soldering or welding. This provides mechanical support for the exchanger tubes 20 on the housing cover 60.

[0042] In a preferred embodiment, the exchanger tubes 20 consist of thin-walled stainless steel tubes. The exchanger tubes 20 are 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 such that all inlets 22 and all outlets 24 are each arranged in a connected group, so that the heat exchanger 1 according to the invention can be easily connected, for example, to the exhaust system of the motor vehicle. For this purpose, the front of the housing cover 60 forms a mounting interface S, which is essentially flange-like due to the flat design of the housing cover 60. For mounting the heat exchanger 1 on the motor vehicle, additional small threaded holes 53 are formed in the casing part 50, which have an inner diameter that is smaller than the large threaded holes 55.Corresponding through-holes 63 are formed in the metal bead seal (seal 52) and in the housing cover 60. These allow the heat exchanger 1 to be connected to a plurality of... Fig. 1 screws not shown are connected to the exhaust and coolant system of the vehicle.

[0043] The casing part 50 forms, in addition to the interior space 42 in which the bundle of exchanger tubes 20 is arranged, an inlet channel 56 and an outlet channel 58 for a coolant, which can be, for example, coolant from the cooling system of the internal combustion engine of the motor vehicle. The inlet channel 56 and the outlet channel 58 are arranged such that, during normal operation of the heat exchanger 1, a flow of coolant flows from top to bottom (in Fig. 1) extending flow path through the interior space 42 of the casing part 50, so that the bundle of exchanger tubes 20 is intensively flushed with the coolant. In order to achieve the most intensive interaction possible between the coolant and the surface of the exhaust gas-carrying exchanger tubes 20, a guide plate 36 is also arranged within the legs of the U-shaped exchanger tubes 20. In the illustrated embodiment, this guide plate 36 is again preferably made of stainless steel and is butt-welded or soldered to the housing cover 60, which is also made of stainless steel. The guide plate 36 extends the flow path of the coolant in the interior space 42 of the housing and thus ensures a more intensive thermal exchange between the exhaust gas flowing into the exchanger tubes 20 and the coolant flowing in the interior space 42.

[0044] The inlet channel 56 formed in the shell part 50 and the outlet channel 58 also end in the flange 59 formed by the shell part 50. At the ends of the channels 56 and 58, webs 57 are formed, which form a mechanical support for the metal bead seal (seal 52) resting on the flange 59. This also forms passages 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 therefore be supplied via the front of the housing cover 60 via the coolant inlet 62 and discharged 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 discharged via the outlets 24. In the design shown, this is possible via a single common mounting interface S.

[0045] This is particularly evident from the representation according to Fig. 2, which shows a plan view of a mounting interface S of the heat exchanger 1 in a slightly modified embodiment. The coolant inlet 62 formed in the housing cover 60 and the coolant outlet 64 are clearly visible. The majority of the inlets 22 and outlets 24 of the exchanger tubes 20, however, are shown in the illustration according to Fig. 2 covered by grid structures 23. The arrangement of the inlets 22 and outlets 24 in the housing cover 60 essentially corresponds to that in Fig. 1. Otherwise, the heat exchanger 1 differs according to the illustration of Fig. 2 essentially by the modified arrangement of fastening points 51 on the casing part 50, wherein these fastening points 51 serve to fasten the heat exchanger 1 to mounting structures of the motor vehicle.

[0046] Fig. Figure 3 shows a perspective view of a bundle of exchanger tubes 20 of a heat exchanger 1 in a third embodiment. Compared to the heat exchanger 1 according to Fig. 1, the bundle of exchanger tubes 20 shown here differs essentially in that the exchanger tubes 20 are smooth, e.g. seamlessly drawn thin-walled stainless steel tubes, which do not have a spiral structure 26, as in Fig. 1. In addition, the exchanger tubes 20 are arranged in such a way that they cross each other in pairs, which is achieved at the reversal points of the U-shaped exchanger tubes 20 in Fig. 3 becomes visible.

[0047] Out of Fig. Figure 1 further illustrates how technical measures can prevent unwanted vibrations of the bundle of exchanger tubes 20 in the interior space 42 of the housing. Thus, the guide plate 36, which is mechanically rigidly connected to the housing cover 60 and is arranged within the bundle of exchanger tubes 20, is mechanically firmly connected to the adjacent exchanger tubes 20 at its lateral wall and its bent tip, for example, by soldering or welding. The guide plate 36 thus provides mechanical reinforcement for the internal exchanger tubes 20 of the exchanger tube bundle and thus dampens their vibrations.

[0048] As a further vibration-reducing measure, a bandage 30 is provided, which consists of a stamped stainless steel sheet with a thin wall thickness. This bandage 30 completely surrounds the bundle of exchanger tubes 20 and is mechanically firmly connected to the adjacent exchanger tubes 20 at the contact points, for example by soldering or welding. By enclosing the exchanger tube bundle, the bandage 30 prevents relative vibrations of the outer exchanger tubes 20 to one another. In addition, the bandage 30 forms integrally formed supports 32, which consist of angled projections. These supports 32 provide resilient support for the entire exchanger tube bundle against the inner wall of the housing.

[0049] Finally, stiffening elements 34, which also consist of stamped stainless steel sheet strips, are arranged within the bundle of exchanger tubes 20. These stiffening elements 34 provide mechanically rigid support for the exchanger tubes 20 of the exchanger tube bundle. For this purpose, they are mechanically firmly connected to the exchanger tubes 20, for example, by welding or soldering.

[0050] It should be noted that in individual cases, the mechanically secure connection of the bandage 30 or the stiffening elements 34 to the individual exchanger tubes 20 can be dispensed with. If necessary, the mere form fit between the exchanger tube bundle and the bandage 30 or stiffening element 34 can ensure sufficient support of the exchanger tube bundle and a sufficiently secure fit of the bandage 30 or the stiffening elements 34 on the exchanger tube bundle.

[0051] Fig. 4 shows a plan view of an individual exchanger tube 20 of the heat exchanger 1 according to the first exemplary embodiment. The exchanger tube 20 has a free length designated L, which, depending on the dimensions of the heat exchanger 1, can be in the range between 2 cm and 30 cm. For use in motor vehicles with lower-power internal combustion engines (typically 35-100 kW), typical dimensions of L in the range of 5 cm are suitable. For passenger cars with higher power outputs of 100 kW and above, dimensions in the range of L between 10 cm and 15 cm may be appropriate. For use in trucks, dimensions of L = 20 cm and above may be suitable.

[0052] The exchanger tube 20 has an outer diameter D which is typically in the range between 1 mm and 15 mm, preferably in the range between 6 mm and 12 mm, since this has proven to be particularly suitable for the intended use of the heat exchanger 1 as an exhaust gas heat exchanger for a motor vehicle. As can be seen from Fig. 4 and Fig. 5, which shows a perspective section through the exchanger tube 20 of the Fig. 4, when using stainless steel, values ​​in the range of 0.1 mm to 1 mm are suitable for the wall thickness WS of the exchanger tubes 20, depending in particular 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 is in the range of 0.2 mm to 0.6 mm.

[0053] For the opening width W of the legs of the U-shaped exchanger tubes 20, it has been found that this is preferably greater than or equal to 1.8 times the outer diameter D of the exchanger tube 20. In particular,

[0054] W is greater than or equal to 1.8 x D, whereby it has been found that the opening width W, which is directly correlated with the bending radius R of the U-shaped exchanger tube 20, is W = 2R when a thin-walled tube with a continuous spiral structure 26, for example made of stainless steel or aluminum, is used as the exchanger tube 20. A particularly small opening width W is advantageous for the most efficient use of the interior volume of the housing and is preferable due to the very limited installation space available in a motor vehicle.

[0055] During practical testing, it has been found that particularly favorable properties regarding the turbulence of the exhaust gas flowing through the exchanger tube 20 and thus a particularly intensive heat transfer from the exhaust gas to the wall of the exchanger tube 20 are achieved when the exchanger tube 20 has a spiral structure 26 at least on its inner wall. The winding distance DS of the spiral structure 26 is advantageously between 1 mm and 15 mm, preferably a range between 4 mm and 8 mm. The associated pitch angle is Fig. 4 is designated DW. The height DT of the spiral structure 26 rising from the inner wall of the exchanger tube 20 is advantageously between 1% and 20% of the outer diameter D of the respective exchanger tube 20, with a range between 2.0% and 14% being preferred.

[0056] If a plurality of exchanger tubes 20 is provided, forming an exchanger tube bundle, it has been found that the efficiency achievable during proper use of the heat exchanger 1 is particularly high when the minimum distance between the outer surfaces of the exchanger tubes 20 of the exchanger tube bundle is in the range between 0.5 mm and 5 mm. A range between 1 mm and 2 mm is preferred here, which delivers particularly good results in terms of efficiency when water is used as the coolant.

[0057] In a particularly preferred embodiment, the spiral structure 26 in the exchanger tube 20 is not only formed on the inner surface of the exchanger tube 20. Rather, the spiral structure 26 is created by spirally embossing the outer surface of the exchanger tube 20, with the embossed spiral structure 26 protruding from the inner surface of the exchanger tube 20.

[0058] Fig. 6 schematically shows the angle of rotation α enclosed by the flow path formed in the exchanger tube 20. In the preferred embodiments of the heat exchanger 1 according to the invention, this angle of rotation α = 180°, i.e. the flow direction of the exhaust gas flow exiting the interior 42 of the heat exchanger 1 is 180° opposite to the flow direction of the incoming exhaust gas flow. In other configurations, however, the angle of rotation α can also be smaller or larger than 180°; an angle range between 135° and 225° is generally preferred. The use of exchanger tubes 20 that form a spiral structure 26 on their inner surface has, however, already proven to increase efficiency at an angle of rotation α of 45°.

[0059] Fig. Figure 7 again schematically shows a top view of the inlets 22 and the outlets 24 of a plurality of exchanger tubes 20 arranged as an exchanger tube bundle in the interior 42 of a heat exchanger housing. It can be seen that both the inlets 22 and the outlets 24 are arranged at the grid points of an orthogonal grid.

[0060] An even more efficient use of space results from the arrangement of the inlets 22 and outlets 24 according to Fig. 8. Here, the inlets 22 and outlets 24 are arranged at grid points of a hexagonal grid, meaning that each inlet 22 and outlet 24 is surrounded by six adjacent inlets 22 and outlets 24. In this configuration, the highest possible space filling in the interior 42 of the housing can be achieved by the exchanger tubes 20.

[0061] Fig. 9 shows a section through a housing cover 60 in the region of a bore through which the inlet or outlet end of an exchanger tube 20 is passed. In a preferred embodiment, which has particular advantages in production, the exchanger tube 20 has a support structure 27 at its inlet or outlet end, which forms a mechanical support of the tube end relative to the housing cover 60. This support structure 27 can, for example, be formed from one or more point-shaped projections, in the exemplary embodiment according to Fig. 4, however, it is formed as a circumferential bead. The outer end of the exchanger tube 20 is in the illustrated embodiment according to Fig. 9, so that overall a mechanical support of the exchanger tube 20 on the housing cover 60 results from the combination of the support structure 27 and the flanged end. This support represents a significant 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 fixation of the exchanger tubes 20 on the housing cover 60, for example by means of laser welding spots during a subsequent soldering or welding of the exchanger tube ends to the housing cover 60, can be dispensed with. Fig. The structures shown in Figure 9 can be easily incorporated into the exchanger tube end by inserting an exchanger tube 20 with a uniform inner and outer diameter through the corresponding bore in the housing cover 60. Subsequently, the support structure 27 in the form of a circumferential bead and, at the same time, the flanged edge are created using a suitable tool. The corresponding tool is, for example, a tube expansion tool.

[0062] The sequence of Fig. 10 a to g finally show an exemplary selection of swirl tubes, the structuring of the inner surface of which is suitable for swirling an exhaust gas flow flowing inside, in particular when the flow path which is formed in the at least one exchanger tube 20 of the heat exchanger 1 made from the swirl tube encloses an angle α of more than 45°, in particular of 180°. Fig. 10 a shows again the spiral structure according to Fig. 5 again, which has a constant gradient and a constant structural height DT and is formed in a tube 20 with a constant cross-section over its length.

[0063] Fig. Figure 10 b shows a swirl tube with two essentially identical but counter-rotating spiral structures. Except for a reduced pitch, each of the two spiral structures corresponds to the one shown in Fig. 5. The cross-section of the tube is also essentially constant over its entire length.

[0064] Fig. Figure 10 c shows a swirl tube in which the cross-section of the tube tapers / expands over its length. The spiral structure itself is essentially the same as in Fig. 5 visible structure.

[0065] In contrast, the Fig. 10 f the cross-section of the tube is again essentially constant over its entire length, whereas the pitch of the spiral structure changes over the length of the tube.

[0066] Fig. Figure 10d shows an alternative to the spiral structures of the other structural examples, namely, planar circular depressions in the tube wall, resulting in circular elevations on the inner wall of the tube. Instead of planar circular depressions, annular depressions can also be formed in the wall.

[0067] The swirling structure of the Fig. 10 e is not spiral-shaped; rather, the pipe wall is deformed into rings at regular intervals, resulting in regular constrictions on the inner wall. The depth of the constrictions and / or their spacing can be varied along the length of the pipe.

[0068] Fig. Finally, 10 g shows a swirl tube with an essentially constant cross-section, in whose wall a plurality of identical spiral structures with constant pitch and structure height are introduced.

[0069] Finally, it should be noted that the Fig. 10 a to g can be used not only in isolation, but also in combination with each other within the limits of technical feasibility. In particular, the structural features of the Fig. 10 a to c as well as f and g can be advantageously combined with each other.

Claims

[1] Heat exchanger (1) for the exhaust system of a motor vehicle, comprising a separately formed exhaust gas-carrying exchanger tube (20) which is arranged in a separately formed closed housing through which a coolant flows, said coolant flowing around the outside of the exchanger tube (20), wherein the housing forms at least one housing cover (60) and a casing part (50), wherein the casing part (50) is tightly closed by the housing cover (60), and both ends of the exchanger tube (20) are passed through the housing cover (60) in a gas- and liquid-tight manner, so that the inlet (22) and the outlet (24) of the exchanger tube (20) are arranged outside the housing, and the exchanger tube (20) is bent substantially in a U-shape or semicircular manner between the points at which it is passed through the housing cover (60), and the exchanger tube (20) is designed as a swirl tube, wherein a plurality of exchanger tubes (20) forms a bundle, characterized bythat a guide plate (36) is arranged within the bundle of exchanger tubes (20), which is mechanically firmly connected to the adjacently arranged exchanger tubes (20) at its lateral wall and its bent tip. [2] Heat exchanger (1) according to claim 1, characterized by that the exchanger tube (20) is made of a corrosion-resistant, heat-resistant and flexible material such as stainless steel or aluminum. [3] Heat exchanger (1) according to claim 1, characterized by that the housing cover (60) is made of a material from the same material group (e.g. stainless steel) as the exchanger tube (20). [4] Heat exchanger (1) according to claim 1, characterized by that the casing part (50) is made of a castable material such as aluminium, magnesium, grey cast iron or plastic. [5] Heat exchanger (1) according to claim 1, characterized bythat the casing part (50) consists of a deep-drawable material such as aluminium, magnesium, steel or thermoplastic. [6] Heat exchanger (1) according to claim 1, characterized by that the casing part (50) is designed as a cast part. [7] Heat exchanger (1) according to claim 1, characterized by that a seal (52) is inserted between the casing part (50) and the housing cover (60). [8] Heat exchanger (1) according to claim 6, characterized by that the seal (52) consists of a metallic or other elastic material. [9] Heat exchanger (1) according to claim 1, characterized by that the housing cover (60) and the casing part (50) are designed as separate parts which are connected to one another by means of mechanical holding means. [10] Heat exchanger (1) according to claim 1, characterized bythat the housing cover (60) forms an interface S for connecting the heat exchanger (1) to the exhaust system of the motor vehicle. [11] Heat exchanger (1) according to claim 1, characterized by that the exchanger tube (20) is substantially one-piece between the points at which it is passed through the housing cover (60). [12] Heat exchanger (1) according to claim 1, characterized by that a plurality of exchanger tubes (20) arranged in the housing are provided, which form a bundle connected in parallel in terms of flow technology. [13] Heat exchanger (1) according to claim 11, characterized by that the flow paths of the various exchanger tubes (20) do not touch each other between their respective inlets and outlets. [14] Heat exchanger (1) according to claim 1, characterized by that the exchanger tube (20) is spirally widened or deepened. [15] Heat exchanger (1) according to claim 13, characterized bythat the pitch of a spiral structure (26) is between 1 millimeter and 15 millimeters, preferably between 4 and 8 millimeters. [16] Heat exchanger (1) according to claim 1, characterized by that the exchanger tube (20) is mechanically firmly connected to the housing cover (60) at the point where it passes through the latter. [17] Heat exchanger (1) according to claim 1, characterized by , that a. the heat exchanger (1) forms a coolant inlet (62) and a coolant outlet (64), and b. the coolant inlet (62) and / or the coolant outlet (64) are formed in the housing cover (60). [18] Heat exchanger (1) according to claim 1, characterized by that a flow path extends in the exchanger tube (20), which runs at least within the housing as a winding flow path and there encloses a rotation angle α of at least 135°, preferably of 180°. [19] Heat exchanger (1) according to claim 1, characterized by that the lead-through points (66, 68) at which the exchanger tube (20) is passed through the wall of the housing on the inlet side and outlet side are arranged substantially in a common plane which forms an interface S for connecting the heat exchanger (1) to the exhaust system of the motor vehicle. [20] Heat exchanger (1) according to claim 1, characterized by that the inlet (22) and the outlet (24) of the exchanger tube (20) are arranged substantially in a common plane which forms an interface S for connecting the heat exchanger (1) to the exhaust system of the motor vehicle. [21] Heat exchanger (1) according to claim 1, characterized by that the exchanger tube (20) has an outer diameter D which is between 1 millimeter and 15 millimeters, preferably between 6 millimeters and 12 millimeters. [22] Heat exchanger (1) according to claim 11, characterized bythat the outer surfaces of the exchanger tubes (20) have a minimum distance from each other which is between 0.5 millimetres and 5 millimetres, preferably between 1 and 2 millimetres. [23] Heat exchanger (1) according to claim 12, characterized by that the exchanger tubes (20) are arranged so that they cross each other at least in pairs. [24] Heat exchanger (1) according to claim 12, characterized by that centers of the inlets (22) and / or the outlets (24) lie on the grid points of an orthogonal or hexagonal grid.

Images