EP1413842B1 - Heat exchanger - Google Patents

Description

The invention relates to a heat exchanger, in particular an exhaust gas heat exchanger for a motor vehicle, with pipes and a head piece.

To reduce emissions of an internal combustion engine is known to recirculate exhaust gas to the engine. Due to the high exhaust gas temperatures, the exhaust gas is previously passed through a formed as an exhaust gas cooler heat exchanger to cool the exhaust gas to a temperature favorable for combustion temperature level.

The local exhaust gas cooler is of elongate shape, has at its front ends in each case a bottom, in which the ends of a plurality of tubes are inserted, which are arranged one below the other at a distance. The resulting tube bundle is surrounded by a jacket which is provided with connections through which coolant is supplied and removed.

At the bottom at a front end of the exhaust gas cooler is followed by an approximately funnel-shaped tapered distribution chamber, which communicates with the plurality of tubes. On the opposite side of the floor, the distribution chamber merges into a flange, which is connected to a secondary exhaust pipe.

In such heat exchangers, during operation, when a hot fluid is introduced into the distribution chamber, from where it flows into the tubes, the distribution chamber or a wall enclosing the distribution chamber is heated to a greater extent than, for example, the jacket surrounding the tube bundle, through which coolant flows. The resulting thermal stresses between Verteilkammerwandung and coat call under certain circumstances leaks especially at a contact point between Verteilkammerwandung and coat and have a negative effect on the life of the heat exchanger.

From the US 4,685,292 is known a cooling system for exhaust gases of an engine.

From the US 6,311, C78 B1 a heat exchanger is known, which is integrated in the intake circuit of an internal combustion engine.

The object of the invention is to provide a heat exchanger in which a safe and possibly improved function is ensured.

This object is achieved by a heat exchanger with the features of claim 1.

According to claim 1, a heat exchanger according to the invention comprises a tube block forming tubes, which are flowed through by a first fluid and a second fluid flow around it, so that heat from the first to the second fluid or vice versa transferable. Furthermore, the heat exchanger comprises a head piece, in which there is a distribution chamber communicating with the tubes, so that the first fluid can be distributed to the tubes. The object of the invention is advantageously achieved in that the head at least partially comprises an inner and an outer wall.

The basic idea of the invention is to reduce an immediate transfer of heat from the first fluid flowing into the distribution chamber to the contact area between the head piece and the tube block. This ensures that during operation of the heat exchanger, the temperature difference between the head piece in the contact area and the tube block is smaller than in a one-wall only Head piece, so that less thermal stresses between the head piece and the tube block occur.

Under an inner wall according to the present invention, for example, a guide plate to understand, which is inserted into a head piece according to the prior art. An outer wall is then formed by the prior art header. A gap or cavity occurring between the inner and outer walls causes a thermal insulation between the inner and the outer wall and thus also between the distribution chamber and the outer wall, so that the object underlying the invention is achieved in a very simple manner.

In order to avoid an undesirable back and forth movement of the inner wall relative to the outer wall, according to the invention, the inner and the outer wall are supported against each other with support means. According to the support means are integrated as a knob-like characteristics, as circumferential or interrupted rib or ribs or as deformed statements in the inner and / or in the outer wall, whereby a simple and therefore cost-effective design is possible.

According to the invention, a channel is formed between the inner and the outer wall, which via an inlet opening in the outer wall can be acted upon by a third fluid. The channel can have any shape, but for reasons of space, a flat channel along an inner wall of the outer wall is advantageous.

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

A heat conduction from the inner wall to the outer wall naturally occurs via attachment points between the two walls. Therefore, according to a preferred embodiment, the inner wall is fastened to the outer wall in a region of the head piece facing away from the tubes, so that the distance for the heat conduction from the inner wall to the outer wall in the contact area between the head piece and the tube block is increased and increased warmth Transfer is reduced from the flowing into the distribution chamber fluid to the contact area. Especially with very hot fluids, it is advantageous to provide a heat-resistant connection, such as a welded joint, between the inner and outer walls.

With the third fluid, at least the outer wall is additionally coolable, whereby the contact area between the head piece and the tube block thermally even better decoupled from the first fluid flowing into the distribution chamber. Thus, thermal stresses between the header and the tube block and associated leaks are even better avoided.

According to a preferred development, the third fluid can be conducted through the channel into the distribution chamber and / or into the tubes. The associated mixture of first and third fluid in the heat exchanger, an additional heat transfer and thus improved performance of the heat exchanger is possible. However, a prerequisite for this embodiment is a functional compatibility of the first fluid with the third fluid, for example an equality of the third with the first fluid, and a pressure level of the third fluid that is at least as great as that of the first fluid in the distribution chamber, since the Otherwise, the first fluid exits through the channel from the heat exchanger.

Particularly preferably, the first fluid is an exhaust gas from an internal combustion engine and the third fluid is air. Because of the usually high exhaust gas temperatures during operation, in such a so-called exhaust gas heat exchanger the effect of the basic concept of the invention, namely the reduction of a heat transfer or temperature differences, is particularly great and advantageous.

In another embodiment, the third fluid can be passed out of the channel through an outlet opening in the outer wall. Thereby, the channel in a closed circuit, for example, in a cooling circuit can be integrated, whereby a cooling of the outer wall in a simple manner by means of existing devices, such as the engine cooling circuit, is possible.

Particularly preferably, the third fluid is equal to the second fluid, in particular coolant, whereby cooling of the head piece of cooling of the tube block can be preceded or followed.

Fig. 1:

Einen Wärmeübertrager;

Fig.2:

einen ausschnittsweisen Querschnitt eines Wärmeübertragers nach dem Stand der Technik;

Fig. 3:

einen ausschnittsweisen Querschnitt eines Wärmeübertragers gemäß der vorliegenden Erfindung;

Fig. 4:

einen ausschnittsweisen Querschnitt eines Wärmeübertragers gemäß der vorliegenden Erfindung;

Fig. 5:

einen ausschnittsweisen Querschnitt eines Wärmeübertragers gemäß der vorliegenden Erfindung.

The invention will be explained in more detail by means of embodiments with reference to the drawings. Show it:

Fig. 1:

A heat exchanger;

Figure 2:

a partial cross section of a heat exchanger according to the prior art;

3:

a partial cross section of a heat exchanger according to the present invention;

4:

a partial cross section of a heat exchanger according to the present invention;

Fig. 5:

a partial cross section of a heat exchanger according to the present invention.

In Fig. 1 is a heat exchanger 100, which is used as a coolant-cooled exhaust gas cooler, shown in a broken view. The heat exchanger 100 consists of a tube block 110 which is composed of a plurality of tubes 120 and a jacket 130. The spaced-apart tubes 120 are inserted at the front ends of the tube block 110 in tube sheets, which are not visible except for a circumferential edge 140 from the outside. In order to accommodate the tubes 120 in itself, the jacket 130 is itself tubular and has in its end regions circumferential chambers 150, which are provided with connections 160 for a coolant.

Into the peripheral edge 140 of a tube plate, an approximately funnel-shaped head piece 170 is inserted and welded, so that a non-visible distribution chamber in the head piece 170 communicates with the tubes 120. On the side opposite the tube bottom edge 140, the head piece merges into a flange 180, which can be connected to an exhaust line, not shown.

If an exhaust gas coming from an internal combustion engine flows through the flange 180 into the distribution chamber, the header 170 is heated up considerably due to the usually high exhaust gas temperatures. Subsequently, the exhaust gas flows through the tubes 120 where it can deliver heat to the tube walls. Subsequently, the exhaust gas is collected in another header and led out of the approximately symmetrically constructed exhaust gas cooler. The peripheral chamber 150 of the shell 130 is supplied via the port 160 with a coolant from the cooling circuit of the internal combustion engine, so that the coolant can flow around the tubes 120 and absorb heat from the pipe walls, after which the coolant is led out through a further connection from the exhaust gas cooler.

In an exhaust gas cooler 200 according to the prior art, as in Fig. 2 Sectionally seen in cross-section, the head piece 210 has a wall 220 which is very strongly heated during operation of the exhaust gas cooler 200 due to the direct contact with the hot, flowing into the distribution chamber 230 exhaust gas stream 240. In contrast, the tube block 280 consisting of the tubes 250, the tubesheet 260 and the jacket 270 is directly cooled by the coolant 290, so that the tube block 280 is heated far less than the wall 220 of the header 210.

Due to the associated different thermal expansion of the tube block 280 and the head piece 210 thermal stresses that mechanically stress the weld seam 295, which connects the jacket 270 and the tube plate 260 with the wall 220 of the head piece 210. This can lead to leaks in the region of the weld seam 295 and thus to a shortening of the service life of the exhaust gas cooler 200.

In Fig. 3 a section of a heat exchanger 300 according to the present invention is shown in cross-section. Here, the head piece 310 consists of an outer wall 320 and designed as a guide plate inner wall 330, between which a gap-shaped cavity 325 is formed. The baffle 330 is inserted into the outer wall during manufacture of the exhaust gas cooler 300 and welded, with other attachment methods are conceivable.

The baffle 330 prevents a direct flow of the contact point 340 between the outer wall 320 and the tube block 350 and the tube plate 360 with flowing into the distribution chamber 370 exhaust gas 380. The gap-shaped cavity 325 serves as a kind of thermal insulation between the distribution chamber 370 and the pad 340, so that the outer wall 320 and the contact point 340 are less strongly heated by the exhaust stream 380. This will be thermal Tensions between the header 310 and the tube block 350 are reduced and the risk of leakage is reduced.

The inner wall 330 and the outer wall 320 may be fastened to each other at several points, in particular welded together. In the embodiment in Fig. 3 the walls 320, 330 are advantageously welded together only in a region 390 facing away from the tube block 350 in order to delay as much as possible a heat conduction from the guide plate 330 to the contact point 340 within the material of the head piece 310.

In order to prevent the guide plate 330 from wobbling within the distribution chamber 370, the outer wall 320 and the guide plate 330 are in an area facing the tube block 350 with support nubs 395, which in the exemplary embodiment in FIG Fig. 3 are integrated into the guide plate 330, supported against each other. But just as well, the support nubs can also be integrated into the outer wall 320 or in both walls.

Fig. 4 shows a detail of a further embodiment example of an exhaust gas cooler 400 according to the invention in a cross section. A head 410 in turn consists of an outer wall 420 and an inner wall formed as a guide plate 430, between which a gap-shaped cavity 425 is formed, whereby a contact point 435 between the outer wall 420 and the tube block 440 or the tubesheet 445 is thermally insulated from exhaust gas 455 flowing into the distribution chamber 450.

The inner wall 430 and the outer wall 420 are welded together only in a region 460 facing away from the tube block 440 and are supported against one another in a region facing the tube block 440 with supporting knobs 465 integrated into the inner wall 430. The outer wall has an inlet opening 470, so that the gap-shaped cavity 425 can be acted upon via a connecting flange 475 with air 480.

The communicating with the distribution chamber 450 cavity 425 serves as a flow channel, which leads the air flow 485 between the outer wall 420 and the inner wall 420 in the distribution chamber 450. There, the indicated by the arrow 485 air flow is mixed with the exhaust stream 455, so that an already pre-cooled exhaust gas-air mixture enters the tube block 440. As a result, the exhaust gas as a whole is cooled more effectively and the performance of the exhaust gas cooler 400 is increased.

In order to ensure that the air 480 flows into the exhaust gas cooler 400, care must be taken that the pressure of the air 480 is higher than the pressure of the exhaust gas 455 in the distribution chamber 450. For example to act compressed air or charge air, which is compressed by an air conveyor.

Fig. 5 FIG. 3 illustrates a cross section of a further embodiment possibility for an exhaust gas cooler 500 in the cutout. Here, an inner wall 510 of a head piece 520 is welded to a tube plate 530 and a tube block 540. An outer wall 550 is fixed in a liquid-tight manner to the inner wall 510, for example welded, in a region 560 facing the tube block 540 as well as in a region 570 facing away from the tube block 540.

In addition, the outer wall 550 has a connecting piece 580 for a coolant inlet and a further, not shown connecting piece for a coolant outlet. As a result, the channel 590 formed by the cavity between the inner wall 510 and the outer wall 550 flows through coolant 600 of a cooling circuit.

Although in this embodiment, the contact point 610 between the header 520, the tube sheet 530 and the tube block 540 is located directly on the hot exhaust gas stream 620 in the distribution chamber 630, the temperature difference between the header 520 and the tube block 540 is reduced by the cooling effect of the coolant 600 , Thus, the mechanical stress of the contact point 610 and thus the danger reduced by leaks. In addition, by the additional cooling of the exhaust gas 620, the performance of the exhaust gas cooler 500 is increased.

The present invention has been described using the example of an exhaust gas cooler for a motor vehicle. It is noted, however, that the heat exchanger according to the invention is also suitable for other applications.

Claims (7)

1. A heat exchanger, particularly exhaust gas heat exchanger (100, 300, 400, 500) for a motor vehicle, comprising tubes (120) through which a first fluid can flow and around which a second fluid can flow, and a headpiece (170, 310, 410, 520) in which a distribution chamber (370, 450, 630) that communicates with the tubes (120) is located, wherein at least a portion of the headpiece (170, 310, 410, 520) includes an inner wall and an outer wall (320, 330, 420, 430, 510, 550), characterized in that the heat exchanger further comprises supporting means (395, 465) for supporting the inner wall and the outer wall (320, 330, 420, 430, 510, 550) with respect to one another, and in that a channel (425, 590) forked between the inner wall and the outer wall (320, 330, 420, 430, 510, 550) is capable to receive a third fluid applied via an inlet opening in the outer wall (320, 420, 550).
2. The heat exchanger of claim 1, characterized in that the inner wall (330, 430, 510) is attached, particularly welded to the outer wall (320, 420, 530) in an area of the headpiece (170, 310, 410, 520) that faces away from the tubes (120).
3. The heat exchanger of claim 1, characterized in that the supporting means (395, 465) are integrated in the inner wall and/or in the outer wall (320, 330, 420, 430, 510, 550) and as stud-like embossed areas, as circumferential or noncontinuous rib or ribs, or as shaped deformation.
4. The heat exchanger of claim 3, characterized in that the third fluid can be routed through the channel (425, 590) into the distribution chamber (370, 450, 630) and/or into the tubes (120).
5. The heat exchanger of claim 3 or 4, characterized in that the first fluid is an exhaust gas from an internal combustion engine, and the third fluid is air.
6. The heat exchanger of claim 3, characterized in that the third fluid can be routed out of the channel (425, 590) through an outlet opening in the outer wall (320, 420, 550).
7. The beat exchanger of claim 6, wherein the third fluid is the same as the second fluid, particularly engine coolant.

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