DE102017130094B4 - Exhaust gas heat exchanger and method for operating the exhaust gas heat exchanger - Google Patents

Abstract

Exhaust gas heat exchanger (1) for a motor vehicle, comprising two cooling cassettes (6, 8), each cooling cassette (6, 8) having its own outer housing (5, 7) and a cooling medium being passed around the cooling cassettes (6, 8) and exhaust gas (A) is passed through the cooling cassettes (6, 8), the exhaust gas heat exchanger (1) also having a bypass duct (4) and an inlet diffuser (2) for supplying the exhaust gas (A) and an outlet diffuser (3) for discharging it of the exhaust gas (A) and the cooling medium (15) being fed laterally into the housing (7) and discharged from the housing (5), a transfer point (17) in the inlet diffuser (2) and / or in the outlet diffuser (3) ) is provided for the cooling medium, for the fluid-conducting connection of the first housing (5) to the second housing (7)

Description

The present invention relates to an exhaust gas heat exchanger and a method for operating the exhaust gas heat exchanger.

Exhaust gas heat exchangers are known from the prior art. These are also referred to as EGR coolers or EGR coolers. They are used to reduce the resulting NOx emissions from internal combustion engines in motor vehicles. The exhaust gas heat exchangers reduce the temperature of the recirculated exhaust gas and feed it back into the combustion process. The combustion temperature in the combustion chamber itself drops, which inhibits the occurrence of NOx emissions.

Since the NOx emissions in the combustion process increase as the temperature rises, there is a need for an increased temperature reduction in the recirculated exhaust gases, particularly in the case of modern internal combustion engines with higher performance or performance requirements.

However, different cooling capacities are required in different operating states of the respective internal combustion engine. These are, for example, the cold start phase, city traffic or also on a motorway trip, during which a high output of the internal combustion engine is required over a longer period of time.

Controllable exhaust gas heat exchangers are therefore known from the prior art, which have different cooling capacities or can even be operated in bypass mode, so that initially no exhaust gas cooling takes place at all.

For example, from the DE 10 2008 014 169 A1 a two-stage heat exchanger is known in which hose connections are provided for the passage of a cooling medium and, in this case, a cooling water. The heat exchanger has two cassettes and two housings. However, three different media are passed through the heat exchanger.

The FR 2 982 646 A1 shows an exhaust gas heat exchanger with two cooling cassettes which are arranged in a housing and a separating element is arranged between the two cooling cassettes, which is arranged as a transition point for the passage of the cooling medium from the first to the second cooling cassette. Furthermore, the exhaust gas heat exchanger comprises a valve for bypassing the heat exchanger from the inlet diffuser via a bypass duct to the outlet diffuser.

From the WO 2013/120 998 A2 an exhaust gas heat exchanger with two parallel cooling cassettes is known, each of which has its own housing and a bypass channel. The cooling medium is supplied and discharged via a common supply line and discharge line.

Also is from the EP 2 025 913 B1 a heat exchanger known. Here, two tube bundle heat exchangers are connected in series.

The object of the invention is to provide a compact exhaust gas heat exchanger with different cooling capacities, which also has a simple structure for initial assembly as well as reduced potential weak points in later operation.

The aforementioned object is achieved with an exhaust gas heat exchanger according to the features in claim 1.

A procedural part of the object is also achieved with a method for operating an exhaust gas heat exchanger having the features in claim 10.

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

The exhaust gas heat exchanger for a motor vehicle is characterized in that it has an outer housing and a cooling cassette is arranged in the housing. The cooling cassette can be designed, for example, as a plate heat exchanger, but also as a tube bundle. A cooling medium, preferably cooling water, is now introduced into the housing and in the process flows around the cooling cassette, that is to say is passed around the outside of the cooling cassette. The exhaust gas is passed through the cooling cassette. There is thus an exchange of heat between the cooling medium and the exhaust gas. The exhaust gas heat exchanger also has a bypass duct.

An inlet diffuser for supplying the exhaust gas is provided on an inlet side. An outlet diffuser for discharging the exhaust gas is provided on an outlet side. The cooling medium is fed into and removed from the side of the housing. Appropriate connection points can be available for this purpose.

According to the invention, the exhaust gas heat exchanger is now characterized in that two cooling cassettes are installed in the exhaust gas heat exchanger itself. Each of these cooling cassettes has its own outer housing. In addition, the bypass channel, also called bypass line, is then formed. In each case at the end or at the front diffusers are provided. This is an inlet diffuser on the side where the exhaust gas is fed to the exhaust gas heat exchanger. This is also an outlet diffuser on the side on which the exhaust gas is in turn discharged from the exhaust gas heat exchanger itself. The diffusers are preferably designed as cast components. It is now further provided according to the invention that a transfer point is formed for the passage of the cooling medium from a first cooling cassette into a second cooling cassette. This transfer point is formed in the output diffuser and / or in the input diffuser. The entire exhaust gas heat exchanger is manufactured as a soldered component. The transfer point for the cooling medium is thus an integral part of the diffuser.

The advantage according to the invention is that external hose connections for coupling two different cooling cassettes can be dispensed with. The cooling cassettes are arranged in parallel one above the other or next to one another.

However, because each cooling cassette has its own outer housing, the cooling cassettes can, to a certain extent, depending on the load, expand thermally to different degrees and independently of one another. The number of parts when assembling the exhaust gas heat exchanger according to the invention are reduced. In particular, the integrated transfer point means that there are no leaks or other leaks in this area.

The two diffusers, and therefore the inlet diffuser and the outlet diffuser, are preferably produced as a one-piece cast component made of the same material. The bypass line, the first housing of the first cooling cassette and the second housing of the second cooling cassette are each connected to one another via the inlet diffuser on an inlet side and via the outlet diffuser on an outlet side.

So that a transfer point is now formed for the passage of the cooling medium, a web protrudes in particular on the inlet diffuser and / or on the outlet diffuser. The first housing and the second housing are then arranged on the top and bottom of the protruding web. The web itself has an opening, in particular an elongated hole. This opening then forms the transfer point between the first housing and the second housing. Corresponding to the opening of the web, there are accordingly also openings on the first housing and the second housing, so that the cooling medium, which is in particular cooling water, can pass over here. The opening in the web of the diffuser can also be designed in two parts. This division in two serves the stability of the web itself. The web can be referred to as an extended sheet metal extension or web plate. To produce the opening, the diffuser is first produced as a cast component and then the opening is cut out of the web by mechanical reworking, for example milling. The web also acts as a spacer between the two housings of the respective cooling cassette. The resulting distance between the two housings also serves to compensate for tolerances for accommodating the cooling cassettes in the cast diffuser itself, but also for thermal and local separation.

The individual components of the exhaust gas heat exchanger are soldered together as a whole. The outer housing and the bypass duct are therefore soldered into the respective diffuser. As a result of this soldering process, the area bordering the transfer point can also be soldered at the same time, so that the transfer point is coupled to the respective housing at its outer edges in a fluid-tight manner.

The routing of the cooling medium that is integrated in this way eliminates the need for any other customary external hose or pipe connection. There is also an advantage in terms of installation space, since the entire exhaust gas heat exchanger can be designed to be more compact with fewer components. However, the transfer point is very particularly preferably arranged in the exit diffuser. The cooling medium thus initially flows through a second cooling cassette and passes over to the first cooling cassette at the transfer point, flows through the first cooling cassette and then exits again. The cooling medium can always flow through the entire exhaust gas heat exchanger, that is to say the first housing and the second housing. Depending on the circuit principle, i.e. how the exhaust gas is routed through the exhaust gas heat exchanger, a mutually different cooling output of the exhaust gas heat exchanger can then be provided.

For this purpose, at least one control flap is provided in the inlet diffuser and / or in the outlet diffuser. Two adjustable flaps are particularly preferred in the inlet diffuser. The flaps are arranged centrally in the entrance diffuser. The two adjustable flaps are also preferably mounted about an axis, but are arranged on mutually different sides of this axis.

This makes it possible to operate the exhaust gas heat exchanger in different modes. The invention thus also relates to a method for operating the exhaust gas heat exchanger.

First of all, the exhaust gas heat exchanger can be operated in bypass mode. This is the case in particular, for example, when the internal combustion engine is cold-started. The exhaust gas should thus not be subjected to cooling. The exhaust gas is then passed in particular through the bypass duct.

If a normal cooling capacity of the exhaust gas is required, the exhaust gas can be passed through a cooling cassette. In the cooling cassette, heat is exchanged between the exhaust gas and the cooling medium. The exhaust gas is thus cooled.

If, on the other hand, a greater cooling capacity of the exhaust gas is required, the exhaust gas heat exchanger can be operated in parallel or in a parallel connection. The exhaust gas to be cooled thus flows through both cooling cassettes in parallel. Due to the parallel connection, the exhaust gas flows through a large cross-sectional area, which results in a low pressure loss. In particular for the mono operation described above or the series operation described below.

If an even greater cooling capacity is required, the exhaust gas heat exchanger can be operated in series operation or in a series connection. The exhaust gas is thus first passed through a first cooling cassette via the inlet diffuser and diverted at the outlet diffuser into the second cooling cassette. The exhaust gas then flows through the second cooling cassette. Again in the inlet diffuser, the exhaust gas is then diverted into the bypass duct. Because the cross-sectional area is smaller when the entire exhaust gas flows through one cooling cassette after the other, and the exhaust gas is also deflected at the respective end of the cooling cassette, the pressure loss is higher here.

• 1 einen erfindungsgemäßen Abgaswärmetauscher in einer Längsschnittansicht;
• 2 einen Ausgangsdiffusor mit Übergabestelle in Perspektivansicht,
• 3 eine schematische Längsschnittansicht, in welcher das Kühlmedium durch den Wärmetauscher geführt wird,
• 4 den Abgaswärmetauscher im Bypassbetrieb,
• 5 den Abgaswärmetauscher im Monobetrieb,
• 6 den Abgaswärmetauscher im Parallelbetrieb und
• 7 den Abgaswärmetauscher im Reihenbetrieb.

Further advantages, properties and aspects of the present invention are the subject of the following description. Preferred design variants are shown in the schematic figures. These serve for a simple understanding of the invention. Show it:

• 1 an exhaust gas heat exchanger according to the invention in a longitudinal sectional view;
• 2 an exit diffuser with transfer point in perspective view,
• 3 a schematic longitudinal sectional view in which the cooling medium is passed through the heat exchanger,
• 4th the exhaust gas heat exchanger in bypass operation,
• 5 the exhaust gas heat exchanger in mono operation,
• 6th the exhaust gas heat exchanger in parallel operation and
• 7th the exhaust gas heat exchanger in series operation.

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

1 shows an exhaust gas heat exchanger according to the invention 1 in a longitudinal sectional view. The exhaust gas heat exchanger 1 has an input diffuser on the input side 2 and an output diffuser on the output side 3 on. Between the two diffusers 2 , 3 is a bypass channel 4th arranged. There is also a first housing 5 with a first cooling cassette 6th and a second housing 7th with a second cooling cassette 8th arranged. The cooling cassettes 6th , 8th themselves are designed, for example, as plate or tube bundle heat exchangers, but this is not shown in more detail.

In the exit diffuser 3 is a butterfly valve 9 arranged. In the entrance diffuser 2 are two butterfly valves 10 , 11 arranged around a central axis 12th are pivotable, but on opposite sides of this axis 12th are arranged. There is also a coolant inlet 13th in the area of the second housing 7th the second cooling cassette 8th arranged as well as a coolant outlet 14th on the first housing 5 arranged. Coolant 15th can therefore enter the second housing from the outside 7th are supplied, flows through the second housing 7th and thus flows around the second cooling cassette 8th .

According to the invention is now a web 16 with a central transfer point 17th in the form of an elongated hole between the two housings 5 , 7th educated. The bridge 16 is in one piece and made of the same material on the outlet diffuser 3 educated. This is again in 2 shown in perspective. The bridge 16 stands opposite the diffuser 3 in front of, especially in relation to receiving openings 18th of the diffuser 3 . In the receiving openings 18th can then the housing 5 , 7th according to 1 can be used. Through the bridge 16 is also a distance 21 formed between the first and second housing.

On a circumferential flange 19th of the receiving openings 18th can then the housing 5 , 7th with the diffuser 3 be soldered. Furthermore, on the top and on the bottom of the web 16 also soldered so that the transfer point 17th , here an opening 20th in the form of an elongated hole, the first housing in a fluid-conducting manner 5 with the second housing 7th connects. The coolant 15th then flows through the first housing 5 and flows around the first cooling cassette 6th and occurs at a coolant outlet 14th from the first housing 5 turn off. The coupling can take place via hose connections or pipelines, which, however, are not shown in more detail.

Furthermore, the exhaust gas A. shown, which is on the inlet side through the inlet diffuser 2 flows in and then depending on the position of the butterfly valves 10 , 11 on the bypass channel 4th or the first cooling cassette 6th and / or second cooling cassette 8th is distributed. From the exit diffuser 3 becomes the exhaust A. then merged again and flows out of this.

The inflow and outflow of the coolant 15th is in 3 again shown schematically. It flows through the parallel housings in series 5 , 7th .

4th now shows the exhaust gas heat exchanger 1 in a bypass position. The exhaust A. flows through the entrance diffuser 2 a, flows through the bypass channel 4th and flows at the exit diffuser 3 in turn from the exhaust gas heat exchanger 1 out. The first adjustable flap thus closes on the input side 10 at the entrance diffuser 2 completely the channels for flowing through the cooling cassettes 6th , 8th . The valve is on the exit side 9 also closed in such a way that no exhaust gas A. flows back into one of the cooling cassettes 6th , 8th .

5 now shows a mono circuit. This is the exhaust gas A. only through the lower second cooling cassette 8th guided. The first valve 10 in the entrance diffuser 2 closes the bypass channel for this purpose 4th . The second valve 11 closes the first cooling cassette 6th . The butterfly valve 9 in the exit diffuser 3 also closes the first cooling cassette 6th . The exhaust A. therefore flows through only the second cooling cassette 8th .

6th shows a parallel connection. This will be the first cooling cassette at the same time 6th and the second cooling cassette 8th from the exhaust A. flows through. The first valve is for this purpose 10 in the entrance diffuser 2 the bypass channel 4th arranged closing. The second valve 11 is placed in such a way that it is the first cooling cassette 6th releases. The butterfly valve 9 in the exhaust duct is pivoted here in such a way that it is pivoted upwards and the bypass duct 4th blocked.

According to 7th A series connection is also possible. The exhaust gas flows through this A. first the lower cooling cassette 8th , is then in the area of the output diffuser 3 deflected, flows through the upper cooling cassette 6th and is again in the area of the entrance diffuser 2 deflected and flows through the bypass channel 4th to then get out of the exit diffuser 3 to flow out. Through the positions of the adjustable flaps 10 , 11 and 9 this series connection is possible.

List of reference symbols

1 -

Exhaust gas heat exchanger

2 -

Entrance diffuser

3 -

Exit diffuser

4 -

Bypass duct

5 -

first housing

6 -

first cooling cassette

7 -

second housing

8th -

second cooling cassette

9 -

Control flap to 3

10 -

Control flap for 2

11 -

Control flap for 2

12 -

axis

13 -

Coolant inlet

14 -

Coolant outlet

15 -

Coolant

16 -

web

17 -

Transfer point

18 -

Receiving opening

19 -

flange

20 -

opening

21 -

distance

A -

Exhaust gas

Claims (10)

Exhaust gas heat exchanger (1) for a motor vehicle, comprising two cooling cassettes (6, 8), each cooling cassette (6, 8) having its own outer housing (5, 7) and a cooling medium being passed around the cooling cassettes (6, 8) and exhaust gas (A) is passed through the cooling cassettes (6, 8), the exhaust gas heat exchanger (1) also having a bypass duct (4) and an inlet diffuser (2) for supplying the exhaust gas (A) and an outlet diffuser (3) for discharging it of the exhaust gas (A) and the cooling medium (15) being fed laterally into the housing (7) and discharged from the housing (5), a transfer point (17) in the inlet diffuser (2) and / or in the outlet diffuser (3) ) is provided for the cooling medium, for the fluid-conducting connection of the first housing (5) to the second housing (7) Exhaust heat exchanger (1) after Claim 1 , characterized in that the first cooling cassette (6) has a first housing (5) and the second cooling cassette (8) has a second housing (7). Exhaust heat exchanger (1) after Claim 1 or 2 , characterized in that the bypass line (4) is designed as a separate line. Exhaust gas heat exchanger (1) after one of the Claims 1 to 3 , characterized in that the bypass line (4), the first housing (5) and the second housing (7) are each connected via the inlet diffuser (2) on an inlet side and via the outlet diffuser (3) on the outlet side. Exhaust gas heat exchanger (1) after one of the Claims 1 to 4th , characterized in that the input diffuser (2) and / or the output diffuser (3) are made as a cast component. Exhaust gas heat exchanger (1) after one of the Claims 1 to 5 , characterized in that a protruding web (16) is formed between the first housing (5) and the second housing (7) on the input diffuser (2) and / or on the output diffuser (3) and a protruding web (16) is formed in the web (16) Opening (20), in particular an elongated hole, is formed, which is the transfer point (17). Exhaust gas heat exchanger (1) after one of the Claims 1 to 6th , characterized in that adjustable flaps (9, 10, 11) are provided in the inlet diffuser (2) and / or the outlet diffuser (3). Exhaust heat exchanger (1) after Claim 7 , characterized in that two adjusting flaps (10, 11) are arranged centrally on opposite sides in the inlet diffuser (2). Exhaust heat exchanger (1) after Claim 1 , characterized in that the input diffuser (2), the output diffuser (3), the housing (5, 7) and the bypass channel (4) are soldered to one another. Method for operating an exhaust gas heat exchanger (1) according to at least Claim 1 , characterized in that the exhaust gas heat exchanger (1) can be operated in bypass mode, that the exhaust gas heat exchanger (1) can be operated in series operation, the exhaust gas (A) flowing through the second cooling cassette (8) then flowing through the first cooling cassette (6) and then flows through the bypass (4) and that the exhaust gas heat exchanger (1) can be operated in parallel, in such a way that exhaust gas (A) flows through both cooling cassettes (6, 8) in parallel and that the exhaust gas heat exchanger (1) can be operated in mono mode , such that the exhaust gas (A) only flows through a cooling cassette (8).

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