EP2950031B1 - Exhaust gas heat exchanger made from duplex steel - Google Patents

Description

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

EP2711659 describes such a heat exchanger

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 discharged 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 the to cool exhaust gas arising during the combustion of fuel or to remove heat energy from it.

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.

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 is for a motor vehicle and has an outer shell and plates arranged one above the other in layers one above the other. It is characterized in that an internal lamellar sheet of austenitized steel material in an inner cassette made of ferritic steel material or is arranged from duplex steel and in turn at least two of the inner cassettes are arranged one above the other like a plate and the outer shell is formed around the inner cassettes encompassing duplex steel.

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 lamella plate itself has a wavy or else a sawtooth-shaped configuration in cross-section. 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 in turn makes it possible 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 as well as a cost-effective production, the inner cassette is double-shelled by two shells, 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 a two-shell shell shell, 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 plugged into each other and via a thermal joining process, in particular soldering, coupled together.

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.

In a further preferred embodiment, holders made of duplex steel are arranged on the envelope. By means of these holders, the exhaust gas heat exchanger according to the invention is then 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.

Figur 1

eine Längsschnittansicht durch einen Abgaswärmetauscher und

Figur 2

eine Querschnittsansicht durch einen erfindungsgemäßen Abgaswärmetauscher.

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:

FIG. 1

a longitudinal sectional view through an exhaust gas heat exchanger and

FIG. 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 FIG. 1 and 2 an exhaust gas heat exchanger 1 is shown in longitudinal section and cross-sectional view. According to the invention, the exhaust gas heat exchanger 1 is designed as a plate heat exchanger, wherein a first flow channel 2 is formed between the inner circumferential surface 3 of an outer shell 4 and the outer circumferential surface 5 of the inner cassettes 6 arranged in the shell 4. A second flow channel 7 is then formed in the inner cassettes 6, wherein in each case a fin sheet 8 is also arranged to increase the available there for heat absorption surface. Now, the exhaust gas A flow in the inner cassette 6, wherein a corresponding amount of heat on the lamella 8 and the inner circumferential surface 9 of the inner cassette 6 is received and passed through the wall of the inner cassette 6 to a fluid not shown in detail in the first flow channel 2. According to the invention, a structure is now provided such that the lamination plate 8 is formed of austenitic material, the inner cassette 6 is formed of ferritic material or duplex steel and the sheath 4 of duplex steel. The choice of whether 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.

Furthermore, the sheath 4 is double-shelled and has a first shell 10 and a second shell 11. Again, on the outside of the shell 4, holders 12 are coupled to secure the exhaust gas heat exchanger 1 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 an optimum solder gap 13 is adjusted at a joint to produce a solder seam with a particularly high quality in a subsequent soldering process, so that they just under durability aspects, a high density and resistance to vibration brings with it. The holder 12 itself can be integrally formed on the outside of the shell 4 and material uniform be or be formed in several parts, so that they are coupled by means of a coupling method not shown to the shell 4. Furthermore shown in FIG. 1 and 2 between the inner cassettes 6 and between the outer inner cassette 6 and shell 4 distance hump 14, which may also be in the form of a bulge or a bulge. In particular, the spacer bosses 14 can be introduced by embossing into the respective shell of the inner cassette 6 or the shell 4. 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. Further, 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. These outwardly flared ends 15 are soldered together. As a result, the tightness between the first flow channel 2 and the second flow channel 7 is produced at the edge. The outwardly flared ends 15 also expand during the soldering operation, resulting in a good quality of solder joint therebetween.

Reference numerals:

1 -

Exhaust gas heat exchanger

2 -

first flow channel

3 -

Inner lateral surface to 4

4 -

shell

5 -

Outer lateral surface to 6

6 -

interior cassette

7 -

second flow channel

8th -

lamination plate

9 -

Inner circumferential surface to 6

10 -

first cup to 4

11 -

second bowl to 4

12 -

holder

13 -

solder gap

14 -

distance hump

15 -

End to 6

A -

exhaust

Claims (10)

1. Exhaust gas heat exchanger (1) for a motor vehicle comprising an outer shell (4) and therein plates arranged in layers one above the other, wherein a sheet metal lamella (8) made of austenitic steel material is arranged in an inner cassette (6) made of ferritic steel material or duplex steel and at least two inner cassettes (6) are arranged plate-like one above the other; characterised in that the outer shell (4) is formed of duplex steel encompassing the inner cassettes (6).
2. Exhaust gas heat exchanger according to claim 1, characterised in that a first flow channel (2) is formed between an inner casing surface (3) of the shell (4) and an outer casing surface (5) of the inner cassettes (6).
3. Exhaust gas heat exchanger according to claim 1 or 2, characterised in that a second flow channel (7) is formed in the inner cassettes (6).
4. Exhaust gas heat exchanger according to claim 1 to 3, characterised in that the inner cassettes (6) are formed of a double skin of two shells, wherein the two shells are welded to one another.
5. Exhaust gas heat exchanger according to claim 4, characterised in that the shells of the inner cassettes (6) have outwardly directed spacer studs (14).
6. Exhaust gas heat exchanger according to claim 1 to 5, characterised in that the shell (4) has inwardly directed spacer studs (14).
7. Exhaust gas heat exchanger according to any one of claims 1 to 6, characterised in that the shell (4) as the outer shell (5) is formed of a double skin of two shells (10, 11), wherein the two shells (10, 11) are welded to one another.
8. Exhaust gas heat exchanger according to any one of claims 1 to 7, characterised in that as the duplex steel an alloy with number 1.4462 or 1.4362 or 1.4162 is used.
9. Exhaust gas heat exchanger according to any one of claims 1 to 7, characterised in that on the shell (4) brackets (12) made of duplex steel are arranged.
10. Exhaust gas heat exchanger according to claim 9, characterised in that the brackets (12) are integrally formed with and made from the same material as the shell (4).

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