EP1977185B1 - Heat exchanger for a combustion engine - Google Patents

Description

The invention relates to a heat exchanger for an internal combustion engine according to the preamble of claim 1.

Heat exchangers for cooling recirculated exhaust gas are known from the prior art. In general, exhaust gas cooling involves the problem of the high chemical aggressiveness of the exhaust gas and of the low pH of its condensates. For this reason, only exhaust gas heat exchangers made of austenitic steels with high corrosion resistance existed so far. Such steels generate high material costs and often further consequential costs due to the more complex Bearbeitungsgänge- In addition, austenitic steels are usually poor heat conductors, so that heat exchangers of a given cooling capacity relatively large and heavy build.

The publication JP 2003 222498 A discloses a shell-and-tube heat exchanger with heat transfer elements made from super-ferritic stainless steel.

The publication DE 103 28 846 A discloses a gas cooler with domes made of stainless steel.

The publication US 4,461,811 discloses a ferritic stainless steel.

It is the object of the invention to provide a heat exchanger for cooling exhaust gas or exhaust air mixture of an internal combustion engine, which can be produced at low cost.

This object is achieved according to the invention for a heat exchanger mentioned above with the characterizing features of claim 1.

The fact that at least part of the heat exchanger is made of ferritic steel, costs can be saved due to the generally lower prices for these steels.

In a preferred embodiment, the regularly better thermal performance of ferritic steels is used to a particular extent compared to austenitic steels in that the ferritic part of the heat exchanger is in contact with the fluid. Due to the higher thermal conductivity of the ferritic steel thus a total of a small-sized, material, weight and cost-saving design of a heat exchanger for exhaust gas cooling is possible.

The fluid is particularly preferably a recirculated exhaust gas or exhaust gas / air mixture of the internal combustion engine, the fluid temperature in the first connection region being more than 300 ° C., in particular more than 500 ° C., under normal operation. As a result, the risk of condensation of acidic condensate from the exhaust gas in the region of the entire heat exchanger is reduced.

According to the invention, the ferritic part of the heat exchanger essentially corresponds to the first connection region and is adhesively bonded to the exchanger region. Particularly in the first connection area, the temperatures are particularly high, which is why ferritic steels can be used relatively easily. In addition, ferritic steels usually have a lower coefficient of thermal expansion than austenitic steels, which is why the combination of a ferritic connection region with a subsequent austenitic exchange region is particularly favorable in terms of strain-induced material stresses. In particular in this context, the first connection region preferably has a widening of a passage cross-section in the direction of the exchanger region. Further preferably, an adjustable flap can be arranged in the connection region. By way of example, a distribution of the exhaust gas to a cooled region or a bypass channel can take place through the flap.

In a further preferred embodiment, the exchanger region has a plurality of exchanger tubes. Tube coolers are mechanically very stable and are particularly suitable in connection with a liquid coolant. For this purpose, the exchanger area expediently has an exchanger housing through which the liquid coolant can flow. Since the exchanger housing is not regularly in contact with the exhaust gas, it is particularly appropriate that the exchanger housing is made of ferritic steel, since even in the event of rust through, no liquid coolant gets into the combustion chambers of the engine.

To improve a heat exchanger performance can advantageously be the exchanger tubes made of ferritic steel, since this material has a good heat conduction.

Particularly advantageously, it can be provided that a further part of the heat exchanger consists of a further ferritic steel. There are ferritic steels with different corrosion resistance and mechanical properties, which is reflected regularly in the material price. Depending on the extent to which the part of the heat exchanger in question is exposed to corrosion or involved in heat conduction, the various parts of a heat exchanger may consist of different ferritic steels to optimize costs.

In a further preferred embodiment, the heat exchanger comprises a plurality of disc-like interconnected disc elements. Such a heat exchanger is particularly suitable as exhaust gas heat exchanger. Advantageously, a Berippungselement is arranged between the disc elements, which consists of the ferritic steel. Due to the type of construction, corrosion of the ribbing elements does not regularly entail the risk of a breakthrough of coolant into the fluid area, which would otherwise lead to engine damage due to water hammer. Therefore, in particular separable applicable Berippungselemente for training of ferritic steel are particularly predestined. Such a ribbing element can be arranged in the fluid to be cooled and / or in the coolant. If a ribbing element in both the fluid is arranged as well as in the coolant, so these Berippungseiemente regularly differ in their training.

In this case, a housing which surrounds the disk elements and which consists of the ferritic steel is particularly preferably provided. A high-life corrosion of the housing would not lead to a connection between the coolant and the exhaust gas, whereby the risk of engine damage is reduced. Such a housing is a component of considerable size, in which considerable costs can be saved by using ferritic steel. However, when using a sufficiently corrosion-resistant ferritic steel, it is also preferable for the disc elements to be made of ferritic steel, which serves for the heat conduction and thus the total heat exchanger performance for a given size.

According to the invention, another part of the heat exchanger is made of an austenitic steel, whereby a material with a high corrosion resistance is used at least at critical points. The austenitic steel is preferably a steel from the group 1.4301 and 1.4404. These material designations comply with the standard DIN EN 100 88-2, to which reference is made for all the numbered material designations mentioned in the context of the present invention.

According to the invention, the part made of ferritic steel with the austenitic steel part is glued directly to one another in a materially bonded manner. By such a cohesive connection, a particularly secure connection is guaranteed. Experiments have shown that at least the preferred for the heat exchanger ferritic and austenitic steels are usually easily bonded together cohesively.

Preferably, the ferritic steel is a steel from the group 1.4016. Suitable higher-alloyed ferritic steels with at least 12% Cr content are preferably from the group 1.4000, 1.4002 and 1.4113. Higher alloyed and stabilized steels (with titanium and niobium) are preferred from the group 1.4509, 1.4513, 1.4512 and 1.4520.

In a further preferred heat exchanger, the coolant is gaseous, in particular air. Such exchangers do not harbor the risk of water hammering in the event of corrosion and have particularly high requirements with regard to the heat conduction of the materials in order to achieve a suitable cooling performance. Thus, the use of ferritic steels is suitable.

A heat exchanger according to the invention can be arranged in a low-pressure branch after an exhaust gas turbine (low-pressure EGR). In this arrangement occur lower mechanical loads and temperature differences. Alternatively, however, the heat exchanger can also be arranged in a high pressure branch in front of an exhaust gas turbine.

Further advantages and features of a heat exchanger according to the invention will become apparent from the embodiments described below and from the dependent claims.

It is advantageous that the fluid is a particular recirculated exhaust gas or exhaust-air mixture of the internal combustion engine, wherein the fluid temperature in the section in the usual mode of operation is more than 300 ° C, in particular more than 500 ° C.

It is advantageous that the first connection region has a widening of a passage cross-section in the direction of the exchanger region.

It is advantageous that an adjustable flap is arranged in the connection area.

It is advantageous that the exchanger area has a plurality of exchanger tubes.

It is advantageous that the exchanger region has an exchanger housing through which the coolant can flow.

It is advantageous that the Berippungselement is arranged in the fluid to be cooled.

It is advantageous that the Berippungselement is arranged in the coolant.

It is advantageous that the austenitic steel is a steel from the group 1.4301 and 1.4404, designations according to DIN EN 100 88-2.

It is advantageous that the coolant is gaseous, in particular air.

It is advantageous that the heat exchanger is arranged in a low pressure branch after an exhaust gas turbine.

It is advantageous that the heat exchanger is arranged in a high-pressure branch in front of an exhaust gas turbine.

Fig. 1

zeigt eine räumliche, teilweise aufgeschnittene Ansicht eines ersten Ausführungsbeispiels eines erfindungsgemäßen Wärmetauschers.

Fig. 2

zeigt eine räumliche Explosionsdarstellung eines zweiten Ausführungsbeispiels eines Wärmetauschers.

Fig. 3

zeigt eine schematische Schnittansicht durch einen fertig montierten Wärmetauscher nach Fig. 2.

Hereinafter, two preferred embodiments of a heat exchanger according to the invention will be described and explained in more detail with reference to the accompanying drawings.

Fig. 1

shows a spatial, partially cutaway view of a first embodiment of a heat exchanger according to the invention.

Fig. 2

shows a spatial exploded view of a second embodiment of a heat exchanger.

Fig. 3

shows a schematic sectional view through a finished mounted heat exchanger after Fig. 2 ,

The exhaust gas heat exchanger after Fig. 1 is built on the principle of a tube bundle exchanger. He has a first connection area 1 to the feeder of the exhaust gas (or exhaust-air mixture), an exchanger region 2, in which the main part of the heat exchange takes place, and a second connection region 3 for the discharge of the exhaust gas. In the first connection area 1 a controllable by means of an actuator 4 via a mechanism 5 adjustable flap 6 is rotatably supported, by means of which the exhaust gas flow between a bypass channel 7 and a bundle of heat exchanger tubes 8 can be deflected adjustable.

The bypass channel 7 and the exchanger tubes 8 are welded together by means of head elements 9, wherein in addition by a housing shell 10 by welding with the head elements 9 a through-flow of liquid coolant exchanger housing is formed. On the housing shell 10, two connecting pieces 11 are provided for the passage of the liquid coolant through the exchanger housing.

In the described heat exchanger, at least the first connection region 1, which consists of a housing which widens in the direction of the exchanger region 2, consists of a ferritic steel. Appropriately, there is also the housing shell 10 made of this steel.

Depending on the temperature range of the exhaust gas flow, which may depend inter alia on whether the radiator is used in a low-pressure or high-pressure exhaust gas recirculation system, the exchanger tubes 8, the head elements 9 as well as the second connection region 3 may consist of a ferritic steel. Due to the higher risk of condensation in the relatively cool region of the gas outlet, the second connection region 3 is preferably made of a ferritic steel of stainless and stabilized quality, in particular 1.4512 or 1.4509. The exchanger tubes 8 and / or the bypass channel 7 and / or the head elements 9 are in the case in which they are made of ferritic steel, preferably made of stainless and stabilized quality (in particular 1.4512 and / or 1.4509).

In order to save costs, in particular external attachments, such as holding plates, etc., may consist of ferritic steel.

The heat exchanger of the second embodiment ( Fig. 2 ) is designed as a disk heat exchanger. In an outer housing 101, which has a first connection region 102 for connecting a feed for the exhaust gas and a second connection region 103 for connecting a discharge for the exhaust gas, a number of disk elements 104 are arranged. The housing 101 also includes a cover 105, on which there are connections 106, 107 for connection of supply lines and discharges of a coolant. The disk elements 104 and areas of the housing 101 and cover 105 together form the exchanger area of the heat exchanger.

Each of the disk elements 104 is made up of two disks 104a, 104b, wherein a ribbing element 108 is provided between the disks 104a, 104b. The respective upper disk 104a has a nozzle-like bulge 104c, which adjoins the edge of an opening in the lower disk of the subsequent disk element. The individual sockets 104c of the disk elements are aligned with each other and with the terminals 106, 107 of the lid 105. The disk element 104 farthest from the cover has a lower disk 104b which has no apertures. In this way, a total of one of the liquid coolant flow-through cavity is formed by the amount of spaces between each upper plate 104a and lower plate 104b, edge boundaries of the cavities are formed by welding the bent edges 104d of the discs 104a, 104b with each other.

The coolant flows in each of the disc elements between the one, the port 106 associated with the nozzle, and the other, the port 107 associated nozzle. In this case, the ribbing 108 flowed around by the coolant ensures additionally improved heat exchange between the coolant and the disks, in particular turbulence of the coolant being produced.

The intermediate space between two adjacent disk elements 104, defined above all by the height of the connecting piece 104c, is open in each case to the terminal areas 102, 103 of the housing 101 of the heat exchanger at the front side of the disk elements. The exhaust gas flows through these intermediate spaces, wherein it is cooled at the large area cooled by the coolant disc elements 104.

For mechanical stabilization and for cooling the housing 101, the longitudinal edge regions 104d of the disk elements 104 are bent over and lie partially flat against the inner wall of the housing 101 (see in particular FIG Fig. 3 ). In particular, the largest possible possible welding or soldering of the disk elements 104 with the inner wall of the housing 101, so that the housing 101 experiences a sufficient cooling performance.

Preferably, the housing 101 is made of a ferritic steel. It may in particular be a cost-effective steel such as e.g. 1.1169, 1.0461, 1.0462 and 1.0463. In the case of corrosion of the housing part 101, there would be no leakage of liquid coolant into the exhaust gas, which is why the use of the cheaper material is made possible here in the interest of a cost-risk assessment.

To improve the heat exchanger performance, thus also to reduce the size for a given heat exchanger performance, the disk stack 104 and also the lid 105 may consist of a ferritic steel. Since these elements provide a separation between the exhaust gas and the liquid coolant, the ferritic steel is preferably a particularly corrosion-resistant grade, such as 1.4000, 1.4002 or 1.4113 or even a high-grade ferritic steel such as 1.4513 or 1.4520.

As Fig. 3 Also, rib elements 109 may be disposed between the disk elements 104 which are flowed around by the exhaust gas and thus provide an enlarged heat exchange surface. These ribs 109 may be made of ferritic steel. thus provide an enlarged exchanger surface. These ribs 109 may be made of ferritic steel.

Claims (11)

1. A heat exchanger for an internal combustion engine, comprising
   a first connecting region (1, 102) for the supply of a fluid to be cooled, wherein the fluid is at least proportionately composed of exhaust gas of the internal combustion engine,
   a second connecting region (3, 103) for the discharge of the fluid, and
   an exchanger region (2, 101, 104, 105) arranged between the first and the second connecting region with regard to a flow path of the fluid,
   wherein a coolant is able to flow around the exchanger region (2, 101, 104, 105),
   characterised in that
   at least a part of the heat exchanger is composed of ferritic steel, wherein the ferritic part of the heat exchanger corresponds substantially to the first connecting region (1, 102) and is glued to the exchanger region (2, 101, 104, 105) in a firmly bonded fashion,
   wherein a further part of the heat exchanger is composed of an austenitic steel, and
   wherein the part composed of ferritic steel and the part composed of austenitic steel are directly glued to one another in a firmly bonded fashion.
2. The heat exchanger as claimed in claim 1, characterised in that the ferritic part is in contact with the fluid.
3. The heat exchanger as claimed in claim 1 or 2, characterised in that the exchanger region (2, 101, 104, 105) has an exchanger housing (10, 101) through which the coolant can flow, wherein the exchanger housing (10, 101) is composed at least partially of the ferritic steel.
4. The heat exchanger as claimed in one of claims 1 to 3, characterised in that the exchanger region (2, 101, 104, 105) has a plurality of exchanger tubes (8), wherein the exchanger tubes (8) are composed of the ferritic steel.
5. The heat exchanger as claimed in one of the preceding claims, characterised in that a further part of the heat exchanger is composed of a further ferritic steel.
6. The heat exchanger as claimed in one of the preceding claims, characterised in that the heat exchanger comprises a plurality of plate elements (104) which are connected to one another in a stacked manner.
7. The heat exchanger as claimed in claim 6, characterised in that a fin element (108, 109) for increasing a thermal contact is arranged between the plate elements (104), wherein the fin element (108, 109) is composed of the ferritic steel.
8. The heat exchanger as claimed in one of claims 6 or 7, characterised in that a housing (101) which is composed of the ferritic steel and which encompasses the plate elements (104) is provided.
9. The heat exchanger as claimed in one of the preceding claims, characterised in that the ferritic steel is a steel from the group 1.4016.
10. The heat exchanger as claimed in one of the preceding claims, characterised in that the ferritic steel is a steel from the group 1.400, 1.4002 and 1.4113.
11. The heat exchanger as claimed in one of the preceding claims, characterised in that the ferritic steel is a steel from the group 1.4513 and 1.4520.

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