EP1769212B1 - Heat exchanger, especially for motor vehicles - Google Patents

Description

The invention relates to a heat exchanger, in particular for motor vehicles according to the preamble of claim 1.Solch a heat exchanger is, for example JP 2003161589 known. Heat exchangers, especially those for motor vehicles, eg. As coolant radiator, intercooler or radiator are known in various constructions, which were each prevailing for certain periods. For example, today's automotive heat exchangers are predominantly made of aluminum, while in the 50's and 60's, they used non-ferrous metal finned tube cooling systems, with brass tubes with thin copper fins joined into a block and soft soldered. In this system, the tubes are formed as flat or oval tubes and the ribs as flat, flat sheets with passages, which are "threaded" on the pipes. Such flat tube system with flat ribs is for example in the publication " Heat Transfer and Pressure Drop Characteristics of Flat Tube and Louvered Plate Fin Surfaces "by A. Achaichia and TA Cowell, in Experimental Thermal and Fluid Science 1988, pages 147-157 described. Such a system has a relatively low airside pressure drop due to the aerodynamically favorable tube cross section; disadvantageous, however, is the high weight.

In the 1970s, aluminum as a material largely displaced the non-ferrous metal, with two different designs for automotive heat exchangers predominating, namely the mechanically joined and brazed systems. Mechanically joined means that the individual parts of the Heat exchanger such as pipes, ribs, tube sheets and collection or water boxes were not materially bonded, but were added by mechanical means. This reduces the manufacturing costs, and further savings have been achieved by using plastic water boxes. How through the DE-B 28 52 408 as well as the DE-B 28 52 415 Known to the applicant, the plastic boxes are connected by means of a flare and a rubber seal with a tube sheet, which receives the tubes. In mechanically joined systems, the tubes often have a circular cross section, in part also an oval or elliptical or flat oval cross section. The tubes are widened mechanically with respect to the ribs and the tubesheets, so that a sufficient pressure is achieved, which produces the required tightness in the tube / bottom connection and the necessary thermal contact in the tube / rib connection. The expansion takes place in part by an olive-shaped mandrel, which causes a plastic deformation of the tube relative to the rib or Bodendurchzügen which lie resiliently after expansion on the outer circumference of the tube. Such expansion is relatively easy for pipes with circular cross-section, so-called round tubes possible, because there is a uniform distribution of stress over the circumference. The problem is the expansion of oval tubes, in particular flat oval tubes with an elliptical cross section and a ratio of half axes about 3: 1 or 5: 1. When Rippendurchzügen and Bodendurchzügen there is a risk of uneven over the circumference contact pressure, which on the one hand in ribs the Heat conduction or the heat transfer and at Bodendurchzügen the tightness affected. Round pipes, on the other hand, result in higher air resistance. Ribs for round tubes were made by the DE-A 37 28 969 the applicant, wherein the edge of the passage circumferentially distributed tongues for spacing with respect to adjacent ribs. A rib passage for a mechanically joined oval tube system was by the DE-C 34 23 746 known, wherein at the edges of the passages also angled surfaces are provided for spacing. A flat oval rib passage, ie for an elliptical tube with an axial ratio of greater than 3: 1 was by the DE-A 44 04 837 Applicant known, wherein provided for spacing nose formed on the walls of the passages are. The expansion of flat oval tubes for a mechanically joined system is in the DE-C 43 32 768 described by the applicant, wherein the expansion elements are pulled through the oval tubes.

In summary, the mechanically joined systems say that they are cheap to manufacture, less favorable in performance. In addition, the disadvantage is a relatively large pipe wall thickness, which - due to the expansion process - is usually over 0.35 mm for aluminum pipes, while 0.07 mm can not be fallen below for the flat aluminum fin in the rule. The rib passage must maintain its elastic hoop stress after the expansion of the tube, so that the rib thickness can not be minimized arbitrarily. Flat tubes with minimal air resistance are not represented as mechanically joined systems, because no pressure can be generated on the flat straight sides.

Higher performance with lower pressure drop are achieved with brazed flat tube systems and corrugated fins, as they were known by the following publications: US-A 4,693,307 . US-A 3,250,325 or the US-A 5,271,458 , The flat tubes are made of solder-plated sheet metal and welded, and between the flat tubes corrugated aluminum sheets are arranged, which solder with their wave crests on the flat sides of the flat tubes and thereby achieve excellent heat transfer. The production of the blocks is carried out by so-called Kassettieren, ie the juxtaposition of flat tubes and corrugated ribs; Thereafter, the cassetted block is compressed transversely to the longitudinal direction of the flat tubes, and tube sheets, provided with passages for the flat tube ends, are plugged. Subsequently, the block is brazed while maintaining the rib tension in a brazing furnace (all parts consist of aluminum or aluminum alloys). The bias of corrugated fins and flat tubes during the soldering process is necessary to achieve a perfect soldering. By brazing results in a solid, inherently rigid block, the corrugated fins in conjunction with outer side members cause a support of the flat tubes, so that they can not bulge under the influence of increased internal pressure. Compared with the The above-mentioned mechanically joined systems give the soldered systems a higher performance (low air-side pressure drop and very good heat conduction between pipe and ribs), but at higher production costs. In this case, limits are set in terms of material thicknesses, with a rib thickness of about 0.05 mm to about 0.07 mm may not be exceeded because of the pressure of the corrugated fins for the soldering - the rib thickness is the distance between adjacent tubes for security against buckling dependent. The cassetting process is also cumbersome and time-consuming because corrugated ribs and flat tubes can not be fitted without aids (fixtures).

By the DE-C 40 15 830 The Applicant has disclosed another brazed flat tube system with corrugated fins for a coolant radiator of a motor vehicle in which flat tubes having a large depth (in the air flow direction) are used.

It is an object of the present invention to reduce the production costs for a heat exchanger of the type mentioned at least the same power.

This object is solved by the features of claim 1. According to the invention, flat tubes and flat ribs with openings are provided for a soldered block, which are penetrated by the flat tubes, the term "flat tubes" in the description as well as in the claims of the present application also being understood to mean slightly ovalized (domed) flat tubes , ie those with slightly curved longitudinal sides. The plate-shaped ribs are thus threaded onto the flat tubes and soldered to them, for which purpose contact surfaces are provided at the openings of the ribs, through which the cohesive connection after soldering and thus an excellent heat transfer between ribs and flat tubes is produced. Preferably, ribs and tubes are made of aluminum or aluminum alloys, which are joined together by a brazing process to form a solid block. This combination of flat tubes and flat ribs on the one hand a minimal air-side pressure drop is achieved and a high heat transfer performance. At the same time the manufacturing costs compared to the conventional flat tube / corrugated fin system are reduced by a simplified Kassettierprozess, namely by "threading" the ribs on the flat tubes. Since the ribs for the soldering process no longer have to fulfill the function of pressing to ensure the finned tube contact, its thickness can be reduced. In addition, due to the system results in the advantage that the tubes offset in the air flow direction to each other, ie can be arranged on a gap. This can increase the performance. The flat tubes may have any depth (in the direction of air flow) relative to their width (transverse to the direction of air flow) and may also be formed as folded multi-chamber tubes, bead tubes or straw tubes. Since the tube cross section in the region of the ribs is in each case completely enclosed by a rib, an inflation due to internal pressure is prevented. It also results in the advantage that the tubes can be made with significantly lower wall thickness, since a widening is eliminated.

In an advantageous embodiment of the invention, the tubes and / or the ribs are provided with a Lotplattierung, which is rolled onto the semifinished material. Commonly used are aluminum-silicon alloys for solder plating. Advantageously, the finned tube block in vacuum, in an inert gas atmosphere or by the so-called Nocolok® method, known by the DE-A 26 14 872 to be soldered.

According to an advantageous embodiment of the invention, the tube ends of the flat tubes can be connected to tube sheets, preferably also by soldering. This results in a solid block on which both sides collecting boxes, z. B. made of plastic and mechanically connected. Likewise, aluminum boxes are possible, so that results in a single-grade all-metal cooler. On the other hand, the tube sheets can also be mechanically connected to the tube ends by means of a rubber seal, this brings the advantage of improved thermal shock resistance. According to the invention, the contact surfaces of the ribs, which enclose the tube, are designed as passages known per se, wherein the passages have a slight conicity. As a result, the pipes can be inserted more easily or the ribs can be threaded more easily, and on the other hand results in a resilient system of Rippendurchzuges on the pipe, ie with a certain bias. After threading the ribs on the tubes to obtain a self-fixed finned tube block, which without further devices, eg. B. clamping means can be soldered.

According to the invention, the contact surfaces can also be used as tabs, ie. H. be formed inclined flaps, which create against the flat longitudinal sides and / or the narrow sides of the tubes and thus produce a bias to hold the flat tubes. However, the contact surfaces are designed so that after soldering results in a closed bond between the rib and flat tube, so that the flat sides of the flat tube are supported by the ribs. Due to the inclination of the tabs or the conicity of the passages results in a Lotspalt, which fills with solder during soldering and forms a solder seam after soldering, which surrounds the tube like a ring and thus causes the required stiffening.

In a further advantageous embodiment of the invention, the passages or tabs may have at their edges angled surfaces or lobes that serve as spacers - or pronounced lugs, which serve as a stop for an adjacent rib. This eliminates additional spacers when threading the ribs.

In a further advantageous embodiment of the invention, the ribs are bekiemt, d. H. they have between the flat tubes on gills or gill fields, which - as known per se - serve to improve the heat transfer. In addition, so-called turbulence generators can be provided in the ribs.

In a further advantageous embodiment of the invention, the wall thicknesses of the tubes and / or the ribs are minimized to a minimum. The wall thickness of the flat tubes can thus be chosen smaller than 0.3 mm, preferably smaller than 0.2 mm, since expansion of the tubes no longer takes place and on the other hand, a support of the flat tubes is given by the ribbed package and the soldering. The material thickness of the ribs can be lowered below 0.07 mm, and preferably below 0.05 mm, because a pressure as in corrugated ribs in the invention is not provided.

According to an advantageous embodiment, a distance of the axes of the flat tubes or slightly ovalized tubes is at least four times as large as the inside diameter, i. the smaller inner diameter of a pipe. This can reduce the weight and material costs of the heat exchanger.

According to a preferred embodiment, a distance of the axes of the flat tubes or slightly ovalized tubes is at most twenty times, more preferably at most ten times as large as the inside diameter of a tube. As a result, a pressure drop of the heat exchanger can be reduced.

According to an advantageous embodiment, a ratio of the rib density (in ribs per decimeter) to the rib expansion in the main flow direction of the second medium (in millimeters) in the range of 2.5 to 8, particularly advantageously in the range of 3 to 6. This may be the weight and the material costs of the heat exchanger are lowered.

Fig. 1

einen Ausschnitt eines Rippenrohrblockes in einer Draufsicht,

Fig. 2

den Rippenrohrblock gemäß Fig. 1 in einer Ansicht von vorn,

Fig. 3

eine Rohr/Rippen-Verbindung als Einzelheit (vor dem Löten),

Fig. 4

eine Lötverbindung zwischen Rippe und Rohr und

Fig. 5

die Lötverbindung zwischen Rippe und Rohr als Einzelheit.

An embodiment of the invention is illustrated in the drawing and will be described in more detail below. Show it:

Fig. 1

a section of a finned tube block in a plan view,

Fig. 2

according to the finned tube block Fig. 1 in a front view,

Fig. 3

a pipe / rib connection as a detail (before soldering),

Fig. 4

a solder joint between the rib and the pipe and

Fig. 5

the solder joint between rib and pipe as a detail.

Fig. 1 shows a section of a finned tube block 1 in a plan view, ie with a view to a substantially flat or flat formed arranged in the plane of rib 2, which is rectangular in shape and has a leading or leading edge 2a and a trailing or trailing edge 2b; the direction of air flow is indicated by arrows L, but may also be in the reverse direction, indicated by a dashed arrow L. The rib 2 is penetrated by a series of flat tubes 3, which have a depth T _ro in the air flow direction and a width B transverse to the air flow direction. The depth of the rib T _ri is greater than the depth of the tube, ie the flat tube 3 is enclosed on the inflow and outflow side of the rib 2.

Between the flat tubes 3 gills 4 are arranged in the rib 2, which form a gill field. In addition, to improve the air-side heat transfer turbulence generator 5 are cut into the rib 2 - these also have the function of spacers. The illustrated section of the finned tube block 1 thus represents a single-row flat tube system. However, the invention is not limited to single-row systems, but also extends to multi-row systems in which the flat tubes in the air flow direction either aligned or offset, that can be arranged on a gap. Also conceivable are so-called monoblock configurations, in which two or more different heat exchangers are combined to form a block, such. B. in the DE-A 195 43 986 the applicant described. The flat tube cross-sections of the individual heat exchanger, z. B. a coolant radiator and a refrigerant condenser have different cross-sections.

Fig. 2 shows the finned tube block 1 in a front view, ie seen in the air flow direction (the scale in Fig. 2 does not match the scale in Fig. 1 ). The continuous ribs 2 are arranged parallel to one another and form a ribbed packet 2 ', which is penetrated by the flat tubes 3. Between the flat tubes 3 there are the gill fields 4 which can be overflowed or flowed through by the air.

Fig. 3 shows a detail of the finned tube block 1, namely the connection of rib 2 and flat tube 3, which has a longitudinal axis 3 'and is shown with its width B. The ribs 2 are - as mentioned - essentially flat and flat or plate-shaped and extend perpendicular to the tube longitudinal axis 3 '. The ribs 2 have so-called passages or collar 6, which are formed from the material of the ribs 2 by known methods, for. As by slitting, tearing, punching and / or embossing - as partially described in the prior art mentioned above.

The collars 6 surround the tube 3 preferably over the entire circumference and provide a mechanical contact between the rib 2 and tube 3 ago. The passages 6 are preferably conical, d. H. they have an acute angle α relative to the outer wall of the flat tube 3. Such a slope on the one hand favors the threading of the tubes 3 and the threading of the ribs 2 on the tubes 3 and on the other hand an elastic conditioning of the collar 6 on the tubes 3. For distance support of rib 2 to rib 2, the collar optionally also shaped noses. 7 (shown in dashed lines), as known from the aforementioned prior art. When threading the ribs 2 on the flat tubes 3 thus a constant distance between the ribs 2 is maintained and ensures a parallelism of the ribs 2. The height of the collar 6 need not be constant over the entire circumference - sometimes this is not possible depending on the geometry of the flat tube cross-section for punching technical reasons, for example, if the rib spacing a should be greater than half the flat tube width (B / 2). For the assembly of the block 1 is important that between the Rippendurchzügen 6 and the flat tubes 3 is a certain adhesion, so that the finned tube block 1 is a solid transportable structure.

4 and FIG. 5 show ribs 2 and tubes 3 are made of aluminum or an aluminum alloy and - which is not shown - with a Lotplattierung, preferably made of an aluminum-silicon alloy. The plating is applied to the semifinished sheets, which are used as starting material for the ribs. and / or pipe production, rolled as a thin layer. After assembly of the finned tube block 1 (see. Fig. 3 ) This is - spent substantially without further aids such as fixtures or the like - in a brazing furnace, not shown, and brazed, ie immediately below the melting temperature of the base material of the rib and tube. The solder flows during the soldering process in the conical annular gaps between the pipe 3 and passage 6 (angle α in Fig. 3 ) and fill them with solder. A corresponding Lotmeniscus or a Lotnaht 8 is in Fig. 5 shown.

The flat tube 3 is - as in 4 and 5 represented by the arrows P - completely enclosed by the rib 2 and the passage 6, so that there is a strong support effect in the form of a rigid T-profile. An "inflation" of the flat tube 3 at internal pressure is thus prevented. The pipe 3 may - as mentioned - made of a sheet and be formed as longitudinally welded or folded pipe, with folded multi-chamber pipes, bead or Noppenrohre are possible. In addition, the tube 3 as extruded, z. B. multi-chamber tube may be formed, wherein the Lotplattierung is then preferably on the rib 2 and the collar 6.

The thickness d of the fin material can be chosen to be relatively low, d. H. less than 0.07 mm, and preferably less than 0.05 mm. Compared to conventional soldered systems, this means a reduction in the rib thickness and thus a reduction in the weight of the finned tube block. Similarly, the wall thickness s of the tubes can be chosen relatively low, d. H. lower than the pipe wall thickness in mechanically joined systems. Preferably, the wall thickness s of the flat tubes 3 is 0.35 mm and less, preferably 0.2 mm and less.

On the finned tube block 1 can - which is not shown here - tube plates, also made of an aluminum material, are placed, wherein the tube sheets have passages for receiving the pipe ends of the flat tubes 3, so that the bottoms can be soldered tightly to the pipe ends. On this finned tube block including tube plates plastic boxes can then be placed, which in a known manner with the tube sheet be connected by a flare connection. As an alternative to plastic boxes, the collecting boxes can also be made of metal, ie of an aluminum material, so that a whole aluminum heat exchanger can be produced with the finned tube block according to the invention.

The soldering of the finned tube block or of the Ganzaluminiumwärmeübertragers can be carried out by various methods, namely in a vacuum, in an inert gas atmosphere or by the so-called Nocolok® process with a non-corrosive flux.

In addition, tube sheets, as is usual in a mechanically joined finned tube block, can be joined by mechanical connection. The pipe ends are inserted through corresponding openings (passages) in the tube sheet; between passages and pipe ends elastomeric seals are arranged. After passing through the pipe ends they are mechanically widened. This results in a solid, but also elastic compound that withstands higher requirements in terms of pressure and thermal shock resistance.

The above-described brazed finned tube block 1 can be preferably used as a coolant radiator or intercooler for automobiles. The pressures occurring in the charge air cooling or in the coolant cooling of an internal combustion engine can be controlled by the brazed system according to the invention.

Claims (17)

1. A heat exchanger, in particular for motor vehicles with a soldered block (1) consisting of flat tubes (3) or slightly ovalised flat tubes and ribs (2), wherein the flat tubes (3) can be flowed through by a first medium and communicate with at least one collecting box and the ribs (2) can be flowed over by a second medium, wherein the ribs (2) are substantially flat and arranged in parallel to one another and have openings with contact surfaces (6) so that the flat tubes (3) are received in the openings and can be soldered in the region of the contact surfaces (6), characterised in that the contact surfaces are formed as conical passages (6) or as slanted tabs (6) which abut the longitudinal sides and/or the narrow sides of the flat tubes (3), wherein the passages (6) or the tabs form a conical soldering gap (α) with the longitudinal sides and/or the narrow sides of the flat tubes (3).
2. The heat exchanger according to claim 1, characterised in that the flat tubes (3) and the ribs (2) can be produced from aluminium or aluminium alloys and can be hard-soldered.
3. The heat exchanger according to claim 2, characterised in that the flat tubes (3) and/or the ribs (2) are solder-plated, preferably provided with an aluminium silicon solder-plating.
4. The heat exchanger according to claim 2 or 3, characterised in that the flat tubes (3) and the ribs (2) can be soldered according to the Nocolok® method.
5. The heat exchanger according to one of claims 1 to 4, characterised in that the flat tubes (3) have tube ends onto which tube bottoms with bottom passages are plugged.
6. The heat exchanger according to claim 5, characterised in that the tube ends can be soldered to the bottom passages.
7. The heat exchanger according to claim 5, characterised in that the tube ends are mechanically joined to the bottom passages, in particular by means of an elastomer seal.
8. The heat exchanger according to one of claims 1 to 7, characterised in that the contact surfaces (6) are formed as spacers for the ribs (2).
9. The heat exchanger according to claim 8, characterised in that the passages (6) or tabs have angled edges or shaped noses (7).
10. The heat exchanger according to one of claims 1 to 9, characterised in that the ribs (2) have gills (4) or gill fields and/or turbulence or whirl generators (5).
11. The heat exchanger according to one of claims 1 to 10, characterised in that the ribs (2) have a material thickness d of d≤0.07 mm, preferably d≤0.05 mm.
12. The heat exchanger as claimed in one of claims 1 to 11, characterised in that the flat tubes (3) have a wall thickness s of s≤0.3 mm, preferably s≤0.2 mm.
13. The heat exchanger according to one of the preceding claims, characterised in that the flat tubes are formed as flat oval tubes with an approximately elliptic cross-section with a large and small half-axis a, b, and with an axis ratio V=a/b and that the axis ratio is V>5:1.
14. The heat exchanger according to one of the preceding claims, characterised in that the flat tubes are formed as welded web tubes.
15. The heat exchanger according to one of the preceding claims, characterised in that the flat tubes are arranged in at least one array.
16. The heat exchanger according to claim 15, characterised in that the flat tubes are arranged flush or offset to one another in an arrangement with several arrays.
17. The heat exchanger according to claim 15 or 16, characterised in that the flat tubes are arranged in two arrays, wherein one array is part of a first heat exchanger, in particular of a coolant cooler, and the other array is part of a second heat exchanger, in particular of a refrigerant capacitor.

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