DE102014106807B4 - Flue gas heat exchanger made of duplex steel - Google Patents

Abstract

An exhaust gas heat exchanger (1) for a motor vehicle comprising an outer shell (4) and plates arranged one above the other in layers, wherein a lamination plate (8) made of austenitic steel material in an inner cassette (6) made of ferritic steel material or duplex steel is arranged and at least two inner cassettes (6 ) are arranged one above the other like a plate and the outer shell (4), the inner cassettes (6) is formed encompassing duplex steel and on the sheath (4) holder (12) are arranged duplex steel.

Description

The present invention relates to an exhaust gas heat exchanger for a motor vehicle according to the features of patent claim 1.

When fuel is burned, the chemical energy contained in the fuel is converted into mechanical energy and heat energy. In the thermodynamic cycle through the ideal Carnot process, the efficiency of an internal combustion engine is limited to about 40%, so that about 60% of the energy contained in the fuel is converted into heat and dissipated with the exhaust gas or via the exhaust stream or the engine block the internal combustion engine are discharged. Exhaust gas heat exchangers are known from the prior art, which are used in internal combustion engines mostly in motor vehicles to cool the exhaust gas produced during the combustion of fuel or to remove this thermal energy.

The exhaust gas has temperatures of more than 500 ° C up to 1000 ° C.

It is now necessary to reduce pollutants in the form of an exhaust gas recirculation or else to remove the heat contained in the exhaust gas and supply, for example, to a thermodynamic cycle, that an exhaust gas heat exchanger is used.

Such an exhaust gas heat exchanger is exposed directly to the high temperatures of the exhaust gas, so that it can lead to significant thermal fluctuations in the operation of the exhaust gas heat exchanger but also in the cold start behavior of an internal combustion engine. In addition, the exhaust gas itself has highly corrosive properties, so that over the duration of the application area corresponding to the material, in particular the lateral surfaces and the coupling points of the exhaust gas heat exchanger are attacked.

A corresponding exhaust gas heat exchanger is for example from the DE 10 2006 029 110 A1 known.

From the EP 2 711 659 A2 a heat exchanger is known which comprises an outer cassette made of austenitic material and in the outer cassette shells made of ferritic material are used. In the shells themselves lamellar sheets made of austenitic material are used. Furthermore, from the WO 2007/014 617 A1 a coiled heat exchanger made of different materials, in which a jacket made of steel and a tube bundle made of aluminum.

Furthermore, from the EP 1 348 924 A2 a plate-type exhaust gas heat exchanger for motor vehicles is known.

Object of the present invention is to reduce an exhaust gas heat exchanger in its component weight and in particular in the production costs, with at least constant or increased use duration and heat transfer properties.

The aforementioned object is achieved in a motor vehicle heat exchanger with the features in claim 1.

Advantageous embodiments of the present invention are the subject of the dependent claims.

The exhaust gas heat exchanger according to the invention for a motor vehicle has an outer shell and plates arranged one above the other in layers. An internal finned sheet of austenitic steel material is disposed in an inner cassette made of ferritic steel material or duplex steel, and again, at least two of the inner cassettes are stacked on top of each other and the outer casing is formed around the inner cassettes of duplex steel. On the shell duplex steel holders are arranged.

Thus, it is possible to provide a plate heat exchanger which has a weight saving of up to 30% and thus an optimal tuning is realized by using different materials. Thus, in particular in the case of the wall thicknesses can be reduced, with at least constant strength and corresponding longevity and corrosion resistance. A possible additional price for the material used in the casing is compensated by the lower percentage use, so that an overall corrosion-resistant exhaust gas heat exchanger is provided. At the same time, the choice of material that is different from one another makes it possible to optimally compensate for different thermal expansions, in particular also taking account of coupling points existing between the components, in particular solder seams.

In the case of the exhaust gas heat exchanger according to the invention, a first flow channel is formed between an inner lateral surface of the shell and an outer lateral surface of the inner cassettes and a second flow channel in the inner cassettes themselves. In order that the surface for a heat transfer is now increased inside the inner cassettes, a lamination sheet is arranged in the inner cassette itself. The slat plate itself points in the Cross-section of a wavy or even a sawtooth configuration. The lamella plate is made of austenitic steel material and positioned in the inner cassette. In a preferred embodiment variant, the lamella plate itself may also be coupled to the inner cassette, for example by a cohesive joining method and in particular a soldering method. This makes it possible, in turn, that the heat energy absorbed via the lamella plate is passed on to the material of the inner cassette, in particular in the coupling points, and then from the inner cassette itself via the wall of the inner cassette to an outer circumferential surface of the inner cassette and an overflowing medium.

In order to realize a simple processability and a cost-effective production, the inner cassette is double-shelled, wherein both shells are soldered together. Both shells essentially have a cross-sectionally U-shaped configuration, wherein these are then plugged into one another in a vertical direction from above and below with the inclusion of the lamination sheet and coupled with a cohesive joining process, in particular a soldering process. At the same time then also the lamellae can be coupled to the inner shell.

So that now two inner cassettes occupy a distance to each other to form a flow channel located therebetween, the inner cassettes have outwardly directed Abstandsbuckel. The respective inner cassettes, which are located completely on the outside, then abut against the inner circumferential surface of the shell with their spacing humps. Optionally, it is possible that the shell also has inwardly directed distance humps. The distance bumps continue to increase the surface area available for each heat exchanger, which further increases the cooling capacity. Furthermore, the ends of the inner cassettes are designed to converge. As a result, the cross section for the entering or exiting exhaust gas is then kept as large as possible in each case on the exhaust gas inlet and outlet side, which benefits a very low pressure loss of the exhaust gas heat exchanger according to the invention. Due to the further reduction in wall thickness due to the use of duplex steel according to the invention, the pressure loss is additionally reduced, with at least the same cooling capacity. The distance hump, which can also be formed as bumps, thereby expanding during a soldering process, so that a high-quality solder joint comes about.

Now, the at least two inner cassettes are then stacked one above the other and positioned in the shell. For this purpose, the sheath is particularly preferably in turn formed as an outer shell of two shells, wherein both shells are soldered together. For this purpose, in turn, the shells of the shell are configured in a U-shaped cross-section and with the respective free ends of the U's plugged into each other and coupled to one another via a thermal joining process, in particular soldering process.

Particularly preferred for the duplex steel of the shell and in the case of the use of duplex steel in an inner cassette for these a duplex steel alloy of 1.4462 or 1.4362 or 1.4162 is used. An optimum of freedom from deformation, corrosion resistance and resistance to the effects of temperature occurs here.

Brazing is preferably used as the brazing process, which in turn is carried out in particular in a continuous or vacuum furnace. A solder additive is used on a nickel-iron basis. As a result, a high corrosion resistance is ensured even when Lotzusatzwerkstoff. The phase balance in the duplex steels does not change as a result of the soldering process. Ferrite and austenite are each present at 50% pro rata. In particular, a soldering temperature between 980 ° C and 1100 ° C.

By means of the holder, the exhaust gas heat exchanger according to the invention is coupled to an internal combustion engine. The holders themselves can be coupled to the casing by materially joining or, preferably, also be formed integrally and with the same material on the casing. In the context of the invention, in particular the components of the shell of the inner cassette and / or the lamella plate are then produced as Blechumformbauteile, in particular deep-drawn components.

Further advantages, features, characteristics and aspects of the present invention are the subject of the following description. Preferred embodiments are shown in the schematic figures. These are for easy understanding of the invention. Show it:

1 a longitudinal sectional view through an exhaust gas heat exchanger and

2 a cross-sectional view through an exhaust gas heat exchanger according to the invention.

In the figures, the same reference numerals are used for the same or similar components, even if a repeated description is omitted for reasons of simplicity.

In 1 and 2 shown is an exhaust gas heat exchanger 1 in longitudinal section and cross-sectional view. The exhaust gas heat exchanger 1 is inventively designed as a plate heat exchanger, wherein a first flow channel 2 between the inner circumferential surface 3 an outer shell 4 and the outer circumferential surface 5 the one in the case 4 arranged inside cassettes 6 is trained. A second flow channel 7 is then in the inner cassettes 6 formed, also to increase the available there for heat absorption surface each a lamination sheet 8th is arranged. Now you can in the inner cassette 6 the exhaust gas A flow, with a corresponding amount of heat through the lamella plate 8th as well as the inner circumferential surface 9 the inner cassette 6 is picked up and over the wall of the inner cassette 6 to a fluid not shown in detail in the first flow channel 2 is passed on. According to the invention, a structure is now provided such that the lamella plate 8th is formed of austenitic material, the inner cassette 6 is made of ferritic material or duplex steel and the shell 4 made of duplex steel. The choice, whether in the inner cassette 6 Duplex steel or ferritic steel material is used, depends on the expected vibration load. If a relatively low vibration load is observed, a ferritic steel material is used, whereas with a high expected vibration load a duplex steel is used.

Further, the case 4 clamshell-shaped and has a first shell 10 and a second shell 11 on. Again on the outside of the case 4 are holders 12 coupled to the exhaust gas heat exchanger 1 to attach to a not shown engine or an internal combustion engine. The first shell 10 and the second shell 11 are each U-shaped in cross-section and inserted into each other in opposite directions, so that at a joint an optimal Lotspalt 13 is set to produce a solder seam with a particularly high quality in a subsequent soldering, so that it brings just under durability issues a high density and resistance to vibration with it. The holders 12 even on the outside of the case 4 be formed in one piece and material uniform or else be designed in several parts, so that these by means of a coupling method not shown to the shell 4 be coupled. Furthermore shown in 1 and 2 between the inner cassettes 6 as well as between outside inner cassette 6 and sheath 4 distance hump 14 , which may also be in the form of a bulge or a bulge. In particular, the distance humps 14 by a stamping process in the respective shell of the inner cassette 6 or the shell 4 be introduced. These then serve to form a spacing of the inner cassettes 6 with each other, which in turn leads to the formation of the respective first flow channel 2 leads. Also at the ends of the inner cassettes 6 are shown in each case to each other outwardly flared tapered ends 15 each two adjacent inner cassettes 6 to each other. Also these outward flared ends 15 are soldered together. As a result, the edge is the tightness between the first flow channel 2 and the second flow channel 7 produced. The outwardly flared ends 15 also expand during the soldering process, resulting in a good quality of intervening solder joint.

LIST OF REFERENCE NUMBERS

1

Exhaust gas heat exchanger

2

first flow channel

3

Inner jacket surface too 4

4

shell

5

Outer jacket surface too 6

6

interior cassette

7

second flow channel

8th

lamination plate

9

Inner jacket surface too 6

10

first shell too 4

11

second shell too 4

12

holder

13

solder gap

14

distance hump

15

End to 6

A

exhaust

Claims (6)

Exhaust gas heat exchanger ( 1 ) for a motor vehicle having an outer shell ( 4 ) as well as layers arranged one above the other in layers, wherein a lamination plate ( 8th ) made of austenitic steel material in an inner cassette ( 6 ) is made of ferritic steel material or of duplex steel and at least two inner cassettes ( 6 ) are arranged one above the other like a plate and the outer shell ( 4 ) the inner cassettes ( 6 ) formed of duplex steel and on the shell ( 4 ) Holder ( 12 ) are arranged from duplex steel. Exhaust gas heat exchanger according to claim 1, characterized in that a first flow channel ( 2 ) between an inner circumferential surface ( 3 ) of the envelope ( 4 ) and an outer circumferential surface ( 5 ) of the inner cassettes ( 6 ) is formed and a second flow channel ( 7 ) in the inner cassettes ( 6 ). Exhaust gas heat exchanger according to claim 1 or 2, characterized in that the inner cassettes ( 6 ) are formed bivalves, wherein both shells are soldered together and in particular the shells and / or the shell ( 4 ) Distance hump ( 14 ) on. Exhaust gas heat exchanger according to one of claims 1 to 3, characterized in that the envelope ( 4 ) as an outer shell ( 5 ) is bivalve-shaped, with both shells ( 10 . 11 ) are soldered together. Exhaust gas heat exchanger according to one of claims 1 to 4, characterized in that as duplex steel, an alloy of the number 1.4462 or 1.4362 or 1.4162 is used. Exhaust gas heat exchanger according to one of claims 1 to 5, characterized in that the holders ( 12 ) in one piece and uniform material on the shell ( 4 ) are formed.

Images