U.S. patent application number 10/953074 was filed with the patent office on 2005-04-21 for heat exchangers comprising winglet tubes, winglet tubes and method for producing same.
This patent application is currently assigned to BEHR GmbH & CO.. Invention is credited to Askani, Hans, Rilk, Martin.
Application Number | 20050081379 10/953074 |
Document ID | / |
Family ID | 34619301 |
Filed Date | 2005-04-21 |
United States Patent
Application |
20050081379 |
Kind Code |
A1 |
Askani, Hans ; et
al. |
April 21, 2005 |
Heat exchangers comprising winglet tubes, winglet tubes and method
for producing same
Abstract
Disclosed is a heat exchanger, in particular for motor vehicles,
having a large number of flat tubes which contain indentations
("winglets") and through which a fluid cooling medium can flow, and
having corrugated fins which are associated with these flat tubes
and to which environmental air or other media can be applied. In
addition, there is disclosed a method for producing flat tubes of
this type ("winglet tubes") and for assembling these flat tubes
into heat exchangers.
Inventors: |
Askani, Hans; (Esslingen,
DE) ; Rilk, Martin; (Pforzheim, DE) |
Correspondence
Address: |
FOLEY AND LARDNER
SUITE 500
3000 K STREET NW
WASHINGTON
DC
20007
US
|
Assignee: |
BEHR GmbH & CO.
|
Family ID: |
34619301 |
Appl. No.: |
10/953074 |
Filed: |
September 30, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60506754 |
Sep 30, 2003 |
|
|
|
Current U.S.
Class: |
29/890.053 ;
165/177 |
Current CPC
Class: |
F28D 1/0535 20130101;
F28F 3/04 20130101; F28F 9/182 20130101; Y10T 29/49391 20150115;
B21C 37/158 20130101; F28F 3/044 20130101; F28D 1/0391
20130101 |
Class at
Publication: |
029/890.053 ;
165/177 |
International
Class: |
F28F 007/00; F28F
001/00 |
Claims
What is claimed is:
1. A method for producing a flat tube for a motor vehicle heat
exchanger, wherein the tube has a central portion and end portions,
comprising: forming a pattern of indentations on a sheet, in areas
that correspond to the central portion and at least one end portion
of a tube to be produced; at least substantially flattening out at
least a portion of the raised surface of at least one indentation
in the area corresponding to the at least one end portion of the
tube, to form an at least substantially flat region on the area of
the sheet corresponding to the at least one end region; and forming
the sheet into the shape of a tube having a substantially flat
region at at least one end portion.
2. A method according to claim 1, wherein said forming comprises a
continuous procedure applied to an endless length of metal sheet,
and the method further comprises cutting the tube in an
intermediate portion of the substantially flat region, to form a
tube having a predetermined length and a substantially flat region
at at least one end portion.
3. A method according to claim 1, wherein the indentations comprise
winglets.
4. A method according to claim 3, wherein the plurality of
indentations comprise a plurality of winglets.
5. A method according to claim 1, wherein the step of forming
indentations comprises forming two linear, parallel indentations
and wherein the step of forming the metal sheet into a tube
comprises forming an hour-glass tube.
6. A method according to claim 1, wherein the step of forming
indentations comprises forming a steg.
7. A tube for a motor vehicle heat exchanger produced by the method
according to claim 1.
8. A tube for a motor vehicle heat exchanger produced by the method
according to claim 4.
9. A tube for a motor vehicle heat exchanger produced by the method
according to claim 5.
10. A tube for a motor vehicle heat exchanger produced by the
method according to claim 6.
11. A method for producing a heat exchanger for a motor vehicle,
comprising: (a) producing a flat tube by a method according to
claim 1; (b) inserting the substantially flat end portion of the
tube into a header; and (c) brazing to form a fluid-tight seal at
the junction between the flat tube and header.
12. A method according to claim 1, comprising producing a plurality
of flat tubes, inserting a plurality of substantially flat ends of
tubes into a header, and brazing to form a plurality of fluid-tight
seals at the junctions between the flat tubes and the header.
13. A heat exchanger produced according to the method of claim
11.
14. A motor vehicle comprising a heat exchanger according to claim
12.
Description
[0001] This application claims priority from U.S. Provisional
Application No. 60/506,754, filed Sep. 30, 2003, which is hereby
incorporated by reference in its entirety, including the
specification, drawings and claims.
BACKGROUND OF THE INVENTION
[0002] The invention relates to a heat exchanger, in particular for
motor vehicles, having a large number of flat tubes which contain
indentations ("winglets") and through which a fluid cooling medium
can flow, and having corrugated fins which are associated with
these flat tubes and to which environmental air or other media can
be applied. The invention further relates to a method for producing
flat tubes of this type ("winglet tubes") and for assembling these
flat tubes into heat exchangers.
[0003] EP 0 030 072 B1 discloses a heat exchanger having a large
number of flat tubes, through which coolant can flow, as well as
corrugated fins which are associated with these flat tubes and to
which environmental air can be applied. In this case, the flat
tubes have indentations, with a very small indentation height. The
indentations point inward on the flat faces of the tubes and are
used to increase the robustness of the flat tubes. A heat exchanger
such as this has the disadvantage that the coolant forms a hot core
flow layer or stream within the flat tubes. This hot core flow is
insulated from the flat tube walls by a cooler wall flow layer and
exchanges little heat. As a result the amount of heat transferred
between the core flow and the flat tube walls is decreased.
[0004] DE 1 96 54 367 A1 relates to the solution of a very
different problem from the field of use of the present invention.
It discloses a rectangular tube for an exhaust gas heat exchanger
equipped with elongated winglets that point inward in the form of
vortex generators. The vortex generators, which are each arranged
in pairs in a V-shape, are formed from the solid material of the
tube and are positioned such that they diverge in the main exhaust
gas flow direction. The vortex generators are used to reduce
deposits on the inner walls of the tubes of solids--such as carbon
black--contained in the exhaust gases. No further details are given
of the dimensions of the vortex generators.
[0005] In commonly assigned German Published Patent Application No.
10127084 A1, which is hereby incorporated by reference in its
entirety, there is disclosed a heat exchanger manufactured from
winglet tubes, in which the indentations extend essentially from
one end to the other of the tubes. By providing sufficient spacing
between perpendicularly transverse rows of indentations, it may be
possible to provide end regions of the tubes that do not have
indentations, in which case the tubes can be snuggly inserted into
the header plate openings and brazed in a fluid-tight manner.
However, design limits not only the number of different lengths of
tubes that can be made (without using different
indentation-producing apparatus) but also the density and/or
configuration of the indentations. For example, in those
embodiments of the commonly assigned application in which the rows
of indentations are obliquely transverse to the tube axis, this
option is not available at all.
[0006] If indentations exist in those regions of the tubes that are
inserted into the header plate, excess brazing material is needed
to secure the connections and/or leak failure points may remain
after the brazing procedure. Although it is theoretically possible
to provide specialized apparatus that can continuously stamp
endless lengths of flat sheet material with intermittently applied
patterns of indentations and thereby produce unstamped regions at
selected locations, e.g., to accommodate different lengths of
tubes, such a solution is completely impractical in terms of mass
production costs, speed and flexibility to accommodate different
tube lengths. Thus, if winglets are formed by indentations in
tubes, the indentations may cause problems with respect to the
forming of sufficiently fluid tight joints between the tube and the
header. Specifically, depending on the dimensions of the
indentation it may be difficult or impossible to form a
sufficiently fluid tight joint by brazing and/or to obtain an
acceptable heat exchanger.
SUMMARY OF THE INVENTION
[0007] Thus, one object of the present invention is to provide an
improved heat exchanger tube of the type that contains
winglets.
[0008] A further object of the invention is to provide an improved
method for producing such improved heat exchanger tubes.
[0009] Another object of the invention is to provide an acceptable
heat exchanger which comprises a fluid tight joint in the
tube/header connection in which tubes contain winglets.
[0010] In accomplishing the foregoing objects, there has been
provided according to one aspect of the invention a method for
producing a flat tube for a motor vehicle heat exchanger, wherein
the tube has a central portion and end portions, comprising:
forming a pattern of indentations on a sheet, in areas that
correspond to the central portion and at least one end portion of a
tube to be produced; at least substantially flattening out at least
a portion of the raised surface of at least one indentation in the
area corresponding to the at least one end portion of the tube, to
form an at least substantially flat region on the area of the sheet
corresponding to the at least one end region; and forming the sheet
into the shape of a tube having a substantially flat region at at
least one end portion.
[0011] According to another aspect of the invention, there is
provided a method for producing a heat exchanger for a motor
vehicle, comprising:
[0012] (a) producing a flat tube by a method as defined above;
[0013] (b) inserting the substantially flat end portion of the tube
into a header;
[0014] and (c) brazing to form a fluid-tight seal at the junction
between the flat tube and header.
[0015] There has also been provided according to the invention both
flat tubes and heat exchangers produced therefrom, where the flat
tubes are made according to the method of the invention.
[0016] Further objects features and advantages of the invention
will become apparent from the detailed description of preferred
embodiments that follows, when considered together with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] In the drawings:
[0018] FIG. 1 shows a three-dimensional partial view of a heat
exchanger according to the invention, having fins, flat tubes and
tube bases;
[0019] FIG. 2 shows a plan view of a first flat face, seen from the
inside of the flat tube;
[0020] FIG. 3 shows a plan view of a second flat face, seen from
inside the flat tube;
[0021] FIG. 4 shows a section illustration of a subregion of the
flat tube, illustrated on a larger scale than in FIGS. 2 and 3;
[0022] FIGS. 5 and 6 show illustrations as in FIGS. 2 and 3 of a
further embodiment;
[0023] FIGS. 7 and 8 show illustrations as in FIG. 2 or 3 of
further embodiments;
[0024] FIG. 9 shows an illustration as in FIG. 7, but with further
details added;
[0025] FIG. 10 shows an illustration as in FIG. 9, but with a
modified geometry;
[0026] FIG. 11 shows an illustration as in FIG. 9, but with a
modified geometry;
[0027] FIG. 12 shows an illustration as in FIG. 9, but with a
modified geometry;
[0028] FIG. 13 shows a section illustration of a flat tube, with
winglets arranged in a stepped form;
[0029] FIG. 14 shows a section illustration of a flat tube, with
winglets arranged in a stepped form;
[0030] FIG. 15 shows a schematic of a method for producing winglet
tubes according to a preferred embodiment of the present
invention;
[0031] FIG. 16 shows a set of rollers including a "stamp out"
roller in a variety of positions;
[0032] FIG. 17a, FIG. 17b, FIG. 17c and FIG. 17d each show
exemplary welded tubes;
[0033] FIG. 18a, FIG. 18b and FIG. 18c each show exemplary folded
tubes; and
[0034] FIG. 19 shows an hour glass tube made by the method
according to the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0035] As discussed in more detail below, the objects of the
invention are accomplished according to the present invention by at
least partially stamping out at least some of the indentations that
have been previously made to produce the winglets, e.g., either
completely or partially selectively flattening at least some of the
winglets, from the end of tubes.
[0036] The term winglet is used in a broad sense to include any
type of indentation that is of sufficient depth to materially
affect the ability to manufacture a fluid-tight connection between
the tube and header plate. The present invention is applicable to a
broad array of types of winglets, including but not limited to the
preferred embodiments that are illustrated in the drawings and
described in more detail hereinafter. According to some of these
preferred embodiments, the indentations are in the form of
elongated winglets with a longitudinal axis, and the ratio between
the height of the winglets and the height of the flat tubes ranges
between approximately 0.05 to 0.5. Further, according to
particularly preferred embodiments, the longitudinal axes of the
winglets may be inclined at angles of approximately 10 degrees to
40 degrees to the direction of the tube longitudinal axis.
Additionally, the adjacent winglets are preferably arranged in (i)
an opposing direction and (ii) transversely with respect to the
longitudinal axis of the tube. The winglets have a height, with
respect to the cross-sectional dimension of the tubes, sufficient
to increase the turbulence of the coolant flow, thereby, depending
on the sizes of the winglets, causing either (i) vortices to be
formed or, at least, (ii) the boundary layer to be broken up. This
improves the exchange between the various coolant layers.
[0037] A further preferred aspect of the invention provides for the
ratio between the height of the winglets and the height of the flat
tubes to be approximately 0.05 to 0.25. Winglets with such
dimensions function primarily to break up the boundary layer of the
coolant flow, thereby ensuring improved exchange between the
various coolant layers, with comparatively low pressure
gradients.
[0038] Another preferred embodiment of the invention provides for
the ratio between the height of the winglets and the height of the
flat tubes to be approximately 0.25 to 0.5. Winglets with such
dimensions deliberately produce longitudinal vortices due to their
height and the elongated form. The winglets are inclined at angles
relative to the tube longitudinal axis. These longitudinal vortices
augment the thorough mixing of the individual coolant layers
downstream because they move in a spiral shape in the tube
longitudinal axis direction, and, thus, have transverse components
in addition to the longitudinal movement.
[0039] An additional preferred aspect of the invention provides for
the winglets to be arranged in winglet rows of, for example, at
least three winglets which run transversely with respect to the
tube longitudinal axis and are preferably essentially in straight
lines. This aspect of the invention also provides, for example, a
number of winglet rows arranged essentially in a straight line one
behind the other in the direction of the tube longitudinal axis.
This arrangement of the winglets, in the form of straight rows,
allows the areas in which longitudinal vortices are produced to be
defined accurately over the entire depth and width of the flat
tube. Such an arrangement makes it possible to optimize the way in
which the longitudinal vortices interact for specific coolant flow
speeds or flow ranges and thereby enhance the thorough mixing. In
this case, it has been found to be particularly advantageous for
the ratio of (i) the distance between the winglet rows in the
direction of the tube longitudinal axis to (ii) the length of the
winglets to be approximately 1 to 10. It has further been found
advantageous for the ratio of (i) the distance between the
winglets, which are transverse with respect to the direction of the
longitudinal axis of the tube to (ii) the length of the winglets to
be approximately 0.1 to 0.9, preferably 0.2 to 0.8. In this
context, the length of the winglets means the length projected
transversely with respect to the tube longitudinal axis.
[0040] A further preferred embodiment of the invention provides for
the capability to arrange the winglets on both flat faces of the
flat tubes and for the respective winglet rows on the first flat
face and on the second flat face to be arranged offset with respect
to one another in the direction of the tube longitudinal axis. An
arrangement of winglet rows such as this allows for mutual
interference between the longitudinal vortices and, hence, further
improvement in the thoroughness of mixing of the coolant layers. In
addition, since the contact surface areas and hence the brazed
surface areas are enlarged, the quality of the brazing between the
flat tubes and the corrugated fins is improved. In this context it
has been found to be particularly advantageous for the ratio
between (i) the distance between the first flat face and the second
flat face of the winglet rows in the direction of the tube
longitudinal axis and (ii) the height of the winglets to be
approximately 10 to 30.
[0041] Yet a further preferred embodiment of the invention provides
for the winglet rows, which are adjacent in the longitudinal
direction, to be arranged offset at an angle, "beta", of
approximately 10 degrees to 30 degrees, preferably at or about 20
degrees. The advantage of an arrangement offset in a manner such as
this is that this results in the indentations forming a uniform
pattern in the tube strip material. This is advantageous for
production and for the fin-tube assembly, particularly its brazing,
to be made more uniform. This can have a positive effect both on
the strength of this joint and on the heat transfer, due to the
homogenization of the heat flows.
[0042] Turning now to the figures, FIG. 1 shows a three-dimensional
partial view of a preferred heat exchanger 10 for use in motor
vehicles, comprising flat tubes 12 through which a liquid coolant
13 can flow. This coolant 13 carries heat from a propulsion unit
(engine), which is normally included but has not been illustrated
here for the sake of clarity, to the heat exchanger 10. The heat
exchanger 10 dissipates this heat via corrugated fins 14 to the
environmental air 15, or to other media. In this case, the
corrugated fins 14 are each arranged between the flat tubes 12, and
the flat tubes are each held by a tube base 16 at their ends. The
tube base 16 in turn forms a part of a collecting tank, which is
normally included but has not been illustrated here for the sake of
clarity. The collecting tank is connected to the internal
combustion engine via hoses.
[0043] The flat tubes 12 of the heat exchanger 10 have a relatively
small flat tube internal height, "H", for example 1 mm, as shown in
FIG. 4, in comparison to a relatively large depth, "t", FIG. 1. In
this case, they have winglets 22 on both their first flat faces 18
and their second flat faces 20. The winglets 22 have a closed
surface and are formed, for example, by rolling in the direction of
the inside of the flat tubes 12. As illustrated in FIG. 2 and FIG.
3, the winglets 22 have an elongated form and are arranged in
winglet rows 24 aligned transversely with respect to the tube
longitudinal axis 13. A number of such winglet rows 24 are arranged
one behind the other in the direction of the tube longitudinal axis
13. The ratio between (i) the distances, b, between the individual
winglets 22 and (ii) the length, L, of the winglets (which is 3 mm,
for example) is preferably, in this case, approximately 0.7,
although this ratio may be in the range from 0.1 to 0.9, and
preferably in the range from 0.2 to 0.8. The width of the winglets,
"B", is preferably 1.3 mm. The ratio between the distances, "C",
between the individual winglet rows 24 and the length, "L", of the
winglets is preferably approximately 4, although this value may be
between 1 and 10.
[0044] The winglets 22 are preferably each inclined at an angle
alpha=20 degrees to the tube longitudinal axis 13, although this
angle may be between 10 degrees and 40 degrees. Winglets 22 which
are, in each case, adjacent transversely with respect to the tube
longitudinal axis 13 are preferably inclined in opposite
directions. Two winglets are thus, in each case, arranged in pairs
in a V-shape, with the two V-limbs diverging from one another in
the direction of the tube longitudinal axis 13. The winglet height,
"h", is approximately {fraction (1/3)} of the flat tube height,
"H", and is preferably 0.2 mm, although this ratio may also be
between 0.3 and 0.7, so that the sum of the respective winglet
heights, "h", of the first flat faces 18 and of the second flat
faces 20 may be greater than the flat tube height, "H". This is
made possible because the individual winglet rows 24 and 24' on the
first flat faces 18 and on the second flat faces 20 are arranged
offset with respect to one another. In this case, the ratio between
(i) the distance between the winglet rows 24 on the two flat faces
18 and 20 and (ii) the winglet height, "h", is approximately
between 10 and 30.
[0045] In an alternate embodiment of the invention which is
illustrated in FIGS. 5 and 6, there are gaps between the winglet
rows 24 so that, for example, pairs of winglets 22 in the row 24
may each be at greater distances from one another than the two
winglets in a pair. Adjacent winglet rows 24 are arranged offset
with a gap in this embodiment.
[0046] Another embodiment of the invention illustrated in FIG. 7
provides for the winglet rows 24 not to extend at right angles to
the tube longitudinal direction, although they do extend
transversely with respect to the tube longitudinal direction, with
the individual winglet rows 24 running parallel to one another.
This results in the uniform distribution of contact points of the
corrugated fins 14 with zones where the heat transfer is high and
is not limited to individual fins, as in the case of an arrangement
at right angles depicted in FIGS. 2 and 3.
[0047] A further embodiment of the invention, illustrated in FIG.
8, provides for the angle of inclination on the outermost winglet
22' to be increased, thus improving the thoroughness of the mixing
in the region of the narrow face of the flat tube 12, where it is
not possible for any winglets to be arranged.
[0048] FIG. 9 shows another preferred embodiment corresponding to
that in FIG. 7, with the winglet rows which are adjacent in the
longitudinal direction being arranged offset at an angle, ".beta.",
of 20 degrees to one another. The distance "C'" between the winglet
rows in this case is preferably 6 mm. Alternatively, as shown in
FIG. 10, it is also possible to use a geometry in which the
winglets 22 are supplemented by winglets 22' arranged between them.
Furthermore, the winglets may also be split geometrically as shown
in FIG. 11, with the winglets 22" which are located in the outer
area being arranged offset with respect to the winglets 22.
[0049] Combinations of the various embodiments are, of course, also
contemplated. In this case, for example, the values relating to the
tube may be related to one face of a beaded tube, separated by a
longitudinal bead.
[0050] FIG. 13 shows an embodiment in which the winglets each have
different heights, "h", relative to one another, resulting in a
rising stepped form seen from inside the tube. By this means the
power density in the central area is further increased, with the
height of the winglets extending overall within the range 10% to
80% of half the height, "H"", of the flat tubes. A descending
stepped form, illustrated as seen toward the inside of the tube in
FIG. 14, is alternatively possible.
[0051] In order to produce tubes comprising winglets as discussed
above, a preferred method provides that sheet metal may be stamped,
for example, by one or more sets of rollers which comprise
raised/recessed surfaces corresponding to a desired winglet
configuration. Most preferably and efficiently, the roll-stamping
step is a continuous process that produces endless lengths of flat
sheet material having a continuous and continuously repeated
pattern of indentations on the flat sheet material, i.e., which can
be used as an intermediate material to produce tubes of any desired
length. In positions along the sheet metal which correspond to the
end regions of a selected final flat tube length, a roll with a
"stamp out element" may be applied such that different geometric
configurations are possible depending on the required tube length.
Stamps having lengths of, for example, 10-100 mm may be used for
the stamp out element. Preferably, individual tubes are formed by
cutting through the central area of the stamped out region, to
produce a stamped out region at the ends of the tube that has a
length between about 5 and 50 mm, respectively.
[0052] Indentations may be formed on a metal sheet by feeding the
metal sheet through at least one set of rollers, referred to below
at the "first set of rollers". At least one of the rollers in the
first set of rollers may comprise at least one selectively raised
surface which at least partially corresponds to an indentation to
be formed on the metal sheet. As the metal sheet passes through the
first set of rollers and the rollers rotate, the raised portion on
the roller stamps the sheet metal thereby forming an indentation in
the metal sheet. As the roller comprising the raised surface or
surfaces continues to roll, it forms additional indentations
periodically along the length of the metal sheet.
[0053] Each indentation formed as the metal sheet passes through
the first set of rollers may or may not be in final form with
respect to, for example, its shape and/or orientation. If an
indentation or indentations are not in final form, the metal sheet
may be fed through one or more further sets of rollers thereby, for
example, progressively changing the shape of the indentation on the
metal sheet. Such further rollers may comprise, for example, a
raised surface and/or surfaces having a height greater than or an
orientation different than a previous set of rollers. As a result,
the rollers progressively increase the height and/or change the
orientation of the indentations on the metal sheet. As an
alternative to the further rollers or following the further
rollers, a set of calibrating rollers may be used to set the
maximum height for all or a portion of the indentations.
Calibration may be accomplished, for example by passing the metal
sheet through a set of rollers arranged so as to have a gap
therebetween, the size of the gap correlating directly or
indirectly to the maximum height of the indentation or
indentations.
[0054] A given roller comprising a raised surface may preferably
comprise a plurality of raised surfaces which may be different from
each other with respect to shape and/or orientation or which may be
substantially identical to each other. The indentations formed on
the metal sheet may comprise, for example, one or more winglets, a
steg and/or indentations for an hour glass tube.
[0055] Once the indentions in/on the metal sheet are in their final
shape/orientation, the metal sheet may be selectively stamped in
one or more regions to selectively substantially flatten all or a
portion of the indentations in the region or regions. Thus, for
example, it is possible that at the edges of the stamped region, a
winglet is partially stamped, e.g., the stamp flattens half of a
winglet. Preferably, the metal sheet is substantially flattened at
regions along the length of the metal sheet which will correspond
to regions at one or both ends of a tube that is to subsequently be
formed from the metal sheet. By "at least substantially flattened"
is meant that the previously formed indentations are either
completely flattened or removed or that they are flattened or
changed in shape to an extent that the remaining indentations do
not materially adversely affect the ability to provide a
fluid-tight seal between the tube and the header plate by brazing.
It is preferred that the indentations are removed as completely as
possible by the substantial flattening step.
[0056] Selective flattening may be accomplished, for example, by
selectively pressing the metal sheet between two plates.
Preferably, the metal sheet is passed between a set of rollers 40,
41 such as those depicted in FIG. 16. At least one roller 40
comprises a raised surface of varying length 42. This varying
length corresponds to the length of the regions that are to be
substantially flattened. The distance between the substantially
flattened regions along the metal sheet may be changed by, for
example, varying the speed at which the roller comprising the
raised surface rotates and/or by varying the diameter of that same
roller. If necessary, a counter-weight of radially lesser dimension
43 can be mounted diametrically opposite to the flattening portion,
to provide for smooth rotation of the roller, while providing a
clearance with respect to the flat sheet and/or the indentations.
FIG. 16 shows a sequence of rotation of rollers 40, 41.
[0057] A substantially flattened region of a metal sheet which
previously contained an indentation is different from a flat region
which never contained an indentation. This is a result of the fact
that the flattening process cannot completely remove the
indentation, or at least not the molecular arrangement of the metal
that was produced by the indentation procedure. As a result, the
substantially flattened region normally contains a shallow
indentation or at least localized deformations in the metal.
Preferably, this profile does not materially adversely affect the
subsequent brazing process. In one preferred embodiment, the
profile has a depth of less than 0.1 mm. While higher indentation
depths are possible, they are increasingly likely to cause problems
and result in a block that is defective.
[0058] After at least substantially flattening regions of the metal
sheet, the sheet is formed into a tube shape, welded along one end
and/or clinched to form a tube, calibrated and then cut
approximately through the central area of the substantially
flattened region to form individual tubes. Cutting is performed at
the substantially flattened regions so that the ends of each tube
comprise a substantially flattened region. These substantially
flattened ends are inserted into headers, and then a substantially
fluid-tight/leakproof seal is formed between the tube and headers
by brazing. It is possible to form the fluid-tight/leakproof seal
because the tubes are substantially flat in the region of
brazing.
[0059] According to one preferred embodiment, the tubes are cut at
a position in the substantially flattened region with a tolerance
of .+-.3 mm.
[0060] FIG. 15 shows a schematic of a method for producing winglet
tubes according to a preferred embodiment of the present invention,
which includes passing sheet metal 30 through stamping roller
station 31, passing the stamped sheet metal to selective flattening
station 32, passing sheet metal from selective flattening station
32 past a sensor 33 arranged with an optional offset relative to
cutting station 34 and then over roller 35. A controller 36 and a
servo regulator 37 may be provided for process control.
[0061] FIGS. 17 and 18 depict different types of welded tubes and
folded tubes that may be formed with winglets and with
substantially flattened or flat end regions according the process
described above. Winglets may be formed on all or part of one or
both sides. The tubes can be made from any type of material that is
suitable, preferably from any metallic material, but also certain
types of plastic materials are subject to hot or cold forming
processes. Preferably, the tubes are made of aluminum or aluminum
alloy. For the sake of simplicity, only some of the tubes are shown
with winglets, and it is possible that the hour glass tube has only
indentations that are continuously formed along the axis of the
tube to form the hour glass profile.
[0062] FIG. 17a depicts an oval flat tube. FIG. 17b depicts an hour
glass tube with a line, X, drawn through the center. FIG. 17c
depicts a rectangular tube, and FIG. 17d depicts a steg tube.
[0063] FIG. 18a depicts a "clinched" rectangular tube. FIG. 18b
depicts a "b-type" tube, and FIG. 18c depicts a "clinched" tube
with an optional "steg."
[0064] An hour glass tube may be formed, for example, by forming
two parallel linear indentions along the length of a metal sheet,
folding the metal sheet in half to form a tube shape with a rounded
bottom to position the two linear indentations across from each
other, welding the top of the sheet to form a rounded top for the
tube and brazing to fill in the gap formed by the opening between
the two indentations. As shown in FIG. 19, a portion of the linear
indentation may be stamped out at the end regions 50 of the hour
glass tube 51 such that, at the end region 52, the tube end is
substantially the same as the ends of the tube labeled "flat tube
(oval)". As a result, a fluid-tight/leakroof seal may be obtained
between the hour glass tube 51 and the header 53.
[0065] As an alternative procedure for realizing the advantages of
the invention, a flat "stamping out" tool with a linear delivery
hub inside the tube welding machine ("Rohrschweissmaschine"), i.e.,
the entire machine, may be used. This approach is less preferred
because it does not permit as high of processing speeds.
[0066] In yet another possible method that can be employed
according to the invention, stamping out is performed as an
additional operation in the heat exchanger block assembly process
("Blockfugeprozess"). Thus, the ends of the tubes are subjected to
a selective tube wall flattening procedure. This approach is
likewise less preferred, since it includes higher costs and offers
the possibility for decreases in process
safety/certainty/reliability.
[0067] In view of this background, an object of the present
invention was to produce a winglet tube with tube ends that are
sufficiently smooth as to not interfere with the brazing
connection, with the stamps/winglets removed, e.g., by being
stamped out. This object is accomplished, preferably, without
requiring additional steps in the block assembly process and/or
core building/assembly process ("Blockfugprozess") at low cost,
without negatively influencing the processing time, without
negatively influencing the time spent in the block assembly process
and/or core building/assembly process, providing maximal
flexibility for the tube length, and providing possible production
speeds of 3 m/s or more.
[0068] As compared to the other possible solutions discussed in the
background supra, the present invention offers a number of
advantages. These advantages include comparatively low capital
costs, high process speeds", flexible/selectable positioning of the
"stamped out" region such that tubes of varying length can be
produced, easily variable stamp length by replacing the stamp out
element on the roller with a different stamp out element,
elimination of an additional operation for the block manufacturing
process.
[0069] The disclosure of German Patent Application No. 100 29
998.9, filed Jun. 17, 2000 is hereby incorporated by reference in
its entirety.
[0070] The foregoing embodiments have been shown for illustrative
purposes only and are not intended to limit the scope of the
invention which is defined by the claims.
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