Note: Descriptions are shown in the official language in which they were submitted.
2167~42
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HEAT EXCHANGER UTILIZING GROMMETS
Background Of The Invention
1. Field of the Invention
This invention relates to heat exchangers and, more particularly, to motor
5 vehicle heat exchangers utilizing grommets in the tube-to-header joints.
2. Desaiption of Related Art
Heat exchangers, particularly those utilized in motor vehicles, may be
liquid-t~air heat exchangers, (e.g., radiators for engine coolant, air conditioning
condensHs and evaporators, and oil coolers) or may be air-to-air heat exchangers10 (e.g. charge air coolers). Liquid-to-air and air-to-air heat exchangers are typically
composed of an inlet tank or manifold, an outlet tank or manifold, and a large
number of tubes extending between the tanks or manifolds which carry the fluid to
be cooled. Headers are normally provided on the tanks for mechanical attachment
and fluid connection of the tubes. Fins attached to the tubes transfer heat between
15 the liquid or gas inside the tubes and the ambient atmosphere outside. A
- mechanical framework or structure is usually included to provide structural strength
to the assembly and to provide means for mounting the unit to the vehicle or other
machinery on which it is used.
As shown in Figs. 1 and 2, a typical heat exchanger core, in this case
20 radiator core 20, is comprised of a plurality of vertical, parallel, spaced tubes 22
between which are interposed heat transfer fins. These fins may be of the flat type
24 or the serpentine type 26 in the composite core depicted in Fig. 1. Any of these
fin styles may include louvers (not shown) to enhance heat transfer. The fins are
typically formed of strips of aluminum, brass, copper or other thermally conductive
25 metal or alloy. Flat fins 24 are generally made of sheet metal which has a collar
formed about a hole. Tubes 22 may be inserted through the collared openings and
a plurality of fins may be stacked in order to make up the fin array within the core.
Serpentine fins may extend in a serpentine pattern wherein the strips are configured
with a plurality of alternating bends between adjacent tubes. The root of the bend
30 is generally secured by brazing or soldering to the tube. A strip portion between
the roots extends between the tubes. In serpentine fins 26 the pattern is similar to
that of a sine wave, while in serpentine fins 30 (Fig. 2) the pattern is zig-zag. The
ends of tubes 22 extend beyond the fin array of core 20 to connect to the headers
and tanks.
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Headers 28a and 28b are at the top and bottom, respectively, of core 20 and
are plates having openings th0ein to receive and seal the upper and lower ends of
the tubes 22. Upper and lower tanks 34a and 34b, respectively, are normally
secured directly to headers 28a and 28b respectively and contain an inlet 36 and5 outlet 38 for the heat exchanger. Side support rails 32 or other structure may be
used to secure the tanks and headers on either side of the core and enable the
completed heat exchanger to be secured within the vehicle or machinery frame.
The tubes utilized may be either round or oval, or may be circular with oval
ends. Prior art methods of welding tube-to-header joints are disclosed, for
10 example, in U.S. Pat. No. 5,407,004, the disclosure which is hereby incorporated
by reference.
In use, heat from the hot liquid or air within generally causes the tubes to
expand and grow in length due to thermal expansion. Since the tanks or manifoldsare fixed with respect to each other by the unit framework or structure, the growth
15 in length of tubes places high mechanical stresses on the tanks and the associated
headers, particularly in the area of the joints between the tubes and headers. In
addition, the pressure of the hot liquid or hot air within the heat exchanger tends to
distort the tanks or manifolds and headers, aeating further stresses on the tube-to-
header joints. The combination of stress resulting from thermal expansion and
20 internal pressure can result in early failure of heat exchangers. Cracks in the joints
between the tubes and the headers are the most common mode of failure. Many
approaches have been taken to avoid heat exchanger failures due to thermal
expansion and internal pressure. Most approaches fall into one or two categories:
1) those which improve the strength of the areas prone to failure and 2) those
25 which provide resilience in the areas prone to failure. Approaches which provide
resilience have appealed to designers because they provide a solution to the
stresses of thermal expansion and internal pressure with a greater economy than
any approach which must provide more material to achieve an improvement in
stl er ~h.
Engine cooling radiators for vehicles have sometimes been designed with
resilient tube-to-header joints. Locomotive radiators have been manufactured by
the assignee of the present invention for over thirty (30) years using headers of
special resilient design as shown in Fig. 3. The headers 28 are made of metal and
have oversized holes or openings in them to receive oval brass tubes 22 extending
from the radiator core. Fins 24 of the flat plate-type design have collars 25 fitted
- 2167S42
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around the tubes. Within the openings in the header there are placed oval brass
ferrules 44. These ferrules are bonded to the header by molded silicone rubber 40.
The ferrules are then soldered to the core tubes extending therethrough to form a
leak-free, resilient joint between the tubes and the headers. While this has been an
5 extremely ef-fective design under typical operating conditions for locomotives, it is
expensive to produce.
In the 1970's, radiators for automobiles were produced which utilized
round aluminum tubes, aluminum plate fins, aluminum headers and plastic tanks.
A sheet of molded rubber provided resilient grommets at each tube hole in the
10 header, and also provided a gasket for sealing the headers to thé plastic tanks,
which were attached to the headers by means of crimped tabs on the headers. The
insertion of the tubes into the rubber grommets in the header holes compressed the
rubber of the grommets providing a resilient sealing attachment of the tubes to the
headers. However, considerable force was required to insert all the core tubes into
15 the header holes simultaneously. This design was limited to relatively small units
because of the problems of core and header distortion during assembly and
because of the close tolerance which was required to accomplish the mating of the
core tubes to the header with the desired amount of grommet compression.
OthH radiators have also utilized rubber grommets in their tube-to-header
20 joints. These radiators have been designed around individual finned tubes having
round ends and oval aoss-sections which are finned along most of their length. As
in the previous design, sealing of the tubes to the header was accomplished by
compression of the grommets between the tubes and the header. However, in this
alternative design, the tubes were assembled to the headers individually thereby25 avoiding high assembly forces. This allowed the construction of very large
radiators for heavy construction equipment. However, the use of tubes with roundends limits this design to cores having rather wide tube spacing which results in
relatively poor thermal performance compared to most radiator core designs.
Lesage U.S. Patent Nos. 4,756,361 and 5,205,354 desaibe a radiator which
30 utilizes tubes which are circular in aoss-section throughout their length. This type
of design is shown in Fig. 4 in which tubes 22 are pressed through collar openings
25 in nat plate fins 24. The tube ends extend through silicone rubber grommets 42
which are disposed in openings within header plate 28. The grommets have a
central peripheral groove and top and bottom lips or flanges which extend outward
35 on the top and bottom of the header plate. Because of its round tubes, this design
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also suffers from poor thermal pe~ rorloance compared to most radiator designs and
must have close tolerances to achieve the required compression of the grommet
between the tube and header opening to seal the joint.
Currently, air-to-air heat exchangers using brazed aluminum cores having
5 oval tubes are being produced. Aluminum headers having oversized oval openingsare welded to cast aluminum manifolds. Oval silicone rubber grommets, otherwise
similar to those described in the Lesage '361 patent, are inserted into the openings
in the headers. These oval grommets may be individual grommets or may be
molded in groups or strips connected by webbing. Because the grommets are
10 designed to have lips or flanges on both sides of the header, insertion of the
grommets into the header holes is difficult and tedious. The ends of the core tubes
are aimped inward slightly to provide for easier entry into the rubber grommets.During the assembly of the core to the header, the core tubes enter the grommetsand the header more or less simultaneously. The force required for assembly is
15 very high because of the compression of the rubber grommets needed between the
tubes and the header for sealing. Additionally, although the openings in the header
are oversized with respect to the tubes, they are smaller than the free outside
dimensions of the unstressed grommet, resulting in distortion of the grommet in the
header hole prior to tube insertion, making assembly of the core tubes to the
20 header very difficult. Also, very close tolerances are required in the core tube and
header hole spacing in order to achieve the desired amount of compression on
each grommet. The combination of these factors makes this type of assembly both
difficult and expensive.
Bearing in mind the problems and deficiencies of the prior art, it is therefore
25 an object of the present invention to provide an improved heat exchanger which
utilizes grommets in the tube-to-header joints.
It is a further object of the present invention to provide an improved method
of assembly of a heat exchanger which utilizes grommets in the tube-to-header
joint.
30It is another object of the present invention to provide a grommet for a heat
exchange tube-to-header joint which may be easily inserted into the header
opening during assembly.
It is a further object of the present invention to provide an improved method
of assembling a core to a header so that all of the tubes may be inserted
35 simultaneously into the header openings without high assembly forces.
2167~2
It is yet another object of the present invention to provide grommets for heat
exchanger tube-to-header joints which do not suffer excessive distortion when
placed in the header openings.
It is yet another object of the present invention to provide an improved
5 method of assembly of headers to the tanks in a heat exchanger.
It is a further object of the present invention to provide an improved method
of assembling fins to tubes in a heat exchanger which utilizes grommets in the
tube-to-header joints.
Summary of the Invention
The above and other objects which will be apparent to those skilled in the
art are achieved in the present invention which provides a heat exchanger
comprising a header for a tank, the header having at least one opening for receiving
a tube from a heat exchanger core; a tube received in and extending through the
15 header opening, and a resilient grommet sealing the tube to the header to prevent
leakage around the tube. The grommet has a body portion extending around a
portion of the tube within the header opening, a radially outwardly extending lip at
a first end of the body portion external to the header opening, and, when
un~l~essed~ a radially inwardly extending lip at a second end of the body portion.
20 The radially inwardly extending lip contacts the tube to form a sealed tube-to-
header joint.
Preferably, the radially inwardly extending lip has an unstressed inner
diameter less than the outer diameter of the tube within the header opening, andwherein the grommet body portion is forced at least partially radially outward
25 sufficient to contact an edge of the header opening. More preferably, at least a
portion of an inner surface of the grommet body portion between the first and
second ends does not contact an outer surface of the tube within the header
opening and the first end of the grommet body portion is forced at least partially
radially inward sufficient to contact the tube. The radially outwardly extending lip
30 may have an outer diameter greater than the diameter of the header opening which
is forced at least partially radially outward sufficient to contact an edge of the
header opening. Consequently, the grommet seals the tube-to-header joint
between: i) an inner surface of the second end of the body portion and an outer
surface of the tube end portion, and ii) an outer surface of the body portion and an
35 edge of the header opening. The grommet body portion, when unstressed, is
" 2167642
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substantially the same as or smaller than the header opening such that the body
portion, when received within the header opening, remains substantially
undistorted by the header.
In another aspect, the present invention provides a method of assembling
5 and sealing a tube-to-header joint in a heat exchanger comprising the steps of:
a) providing a header for a tank, the header having at least one opening
for receiving a tube from a heat exchanger core;
b) providing a tube from a heat exchanger core for insertion within the
header opening;
c) providing a resilient grommet having a body portion for extending
within the header opening, a radially outwardly extending lip larger than the
header opening at one end of the body portion, and a radially inwardly extendinglip at the other end of the body portion, the inwardly extending lip having an
unstressed inner diameter less than the outer diameter of the tube;
d) inserting the grommet into the header opening with the inwardly
extending lip end first; and
e) inserting the tube into the header opening and through the grommet
body portion such that the inwardly extending lip contacts the tube to form a
sealed tube-to-header joint.
Preferably, after step (e), the inwardly extending flange is forced at least
partially radially outwardly by the tube such that the grommet body portion
contacts an edge of the header opening to form a sealed tube-to-header joint and at
least a portion of an inner surface of the grommet body portion between the first
and second ends does not contact an outer surface of the tube within the header
25 opening. Also, the inwardly extending flange may be forced at least partiallyradially outwardly by the tube such that the first end of the grommet body portion
is forced at least partially radially inward sufficient to contact the tube and the
radially outwardly extending lip is forced at least partially radially outward
sufficient to contact an edge of the header opening.
In yet another aspect, the present invention provides a grommet for sealing a
tube-to-header joint in a heat exchanger wherein the header has at least one
opening for receiving a tube end portion from a heat exchanger core. The
grommet has a resilient body portion for extending within the header opening thebody portion, with the inner diameter of the body portion being larger than the
35 outer diameter of the tube end portion. There is also provided a radially outwardly
~ 2167642
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extending resilient flange at one end of the body portion, which outwardly
extending flange is larger than the header opening; and a radially inwardly
extending resilient flange at the other end of the body portion, the innH diameter
of the inwardly extending flange, when unstressed, being less than the outer
5 diameter of the tube end portion. Upon insertion of the grommet into the header
opening and so that the tube end portion extends through the grommet body
portion, the grommet inwardly extending flange is forced at least partially radially
outwardly by the tube end portion such that the grommet body portion is forced at
least partially radially outward sufficient to contact an edge of the header opening
10 to form a sealed tube-to-header joint.
A further aspect of the present invention provides a heat exchanger
comprising a heat exchanger core having at least two tubes having ends extendingoutward from a core body with heat transfer fins being disposed between the tubes.
The fins are formed from a metallic strip which extends in a serpentine pattern
15 between adjacent tubes. The strip is configured with a plurality of alternating
bends such that, within the core body, the root of a bend is secured to a tube and
the strip portion between the roots extends between the tubes. The strip alternating
bend configuration continues to a strip free end near the tube ends where the strip
free end is cut at a root of a bend. Also, the serpentine pattern of the strip portion
20 near the tube ends may be compressed to permit the tube ends to extend outward
from the core body so that the strip free ends contact the header to limit insertion
of the tube ends into the header openings.
Preferably, the heat exchanger core contains a plurality of tubes and heat
transfer fins disposed between the tubes, and substantially all of the strip free ends
25 near the tube ends are cut at the root of a bend. The heat exchanger also
preferably includes at least one tank having a header containing openings for
receiving the tube ends, and resilient grommets within the header openings sealing
the tubes to the header to prevent leakage around the tubes, whereby the strip free
ends contact an end of the grommets.
In another aspect the invention provides a method of manufacturing a heat
exchanger comprising the steps of:
a) providing a heat exchanger core having a plurality of tubes with
spaced tube ends extending outward from the core;
b) providing a tank;
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c) providing a header for the tank, the header having a plurality of
spaced openings for receiving tube ends from the heat exchanger core, the spacing
of the header openings being greater than the spacing of the tube ends;
d) welding the header to the tank and shrinking the length of the header
5 so that the spacing of the header openings conforms to the spacing of the tube ends;
e) inserting resilient grommets into the header openings; and
f) inserting the tube ends into the header openings and through the
grommets to seal the core to the tank.
In its preferred embodiment, the header has a central section with openings
for receiving the tube ends and a pair of flanges connected to, and on opposite
sides of, the header central section. The header flanges have a height of at least
about 2.5 cm and the header is welded to the tank along edges of the flanges
distant from the header central section so that the strength of the connection
15 between the flanges and the header central portion is unaffected by heat generated
during welding of the flanges to the tank.
Brief Description of the Drawings
The features of the invention believed to be novel and the elements
20 characteristic of the invention are set forth with particularity in the appended
claims. The figures are for illustration purposes only and are not necessarily drawn
to scale. The invention itself, however, both as to organization and method of
operation, may best be understood by reference to the detailed desaiption which
follows taken in conjunction with the accompanying drawings in which:
Fig. 1 is a front elevational view of a typical prior art heat exchanger core
and header assembly.
Fig. 2 is a perspective view of a typical assembled radiator of the prior art.
Fig. 3 is a cross-sectional view of a prior art tube-to-header joint which
utilizes molded silicone rubber.
Fig. 4 is a cross-sectional view of a prior art tube-to-header joint which
utilizes grommets.
Fig. 5 is a cross-sectional view of one embodiment of the grommet utilized
in the present invention.
Fig. 6 is a aoss-sectional view of the grommet of Fig. 5 installed in a header
35 opening and receiving a tube end.
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Fig. 7 is a cross-sectional view of the grommet of Fig. 5 installed in a header
opening with the tube fully inserted and sealed.
Fig. 8 is a side elevational view of the grommet of Fig. 5.
Fig. 9 is a top plan view of the grommet of Fig. 5.
Fig. 10 is a top plan view of a header having openings for oval tubes prior to
insertion of the grommet of the present invention.
Fig. 1 1 is an end elevational view of the header of Fig. 10.
Fig. 12 is a cross-sectional view of an alternative embodiment grommet in a
tube-to-header joint.
Fig. 13 is a cross-sectional view of another alternative embodiment grommet
in a tube-to-header joint.
Fig. 14 is an elevational view, partially in cross-section, showing a header
rnated with the tubes and~fins in a core utilizing grommets in the tube-to-header
Joint.
Fig. 15 is an exploded perspective view of the assembly of the tank, header
and grommets of the invention.
Fig. 16 is a perspective view of an assembled charge air cooler made in
accordance with the present invention.
Des~ tion of the Pre~e.,ed Embodiment(s)
This invention is directed primarily toward an air-to-air heat exchanger used
as a charge air cooler, or intercooler, for turbocharged or supercharged engines.
However, it may also be utilized in any other type of heat exchanger, for example,
those discussed in the background of the invention, such as radiators, oil coolers
25 and the like. The present invention provides a heat exchanger which has a resilient
tube-to-header joint to minimize tube-to-header stresses due to a combination of a
thermal expansion of the tubes and internal pressure in the tanks. Preferably oval
tubes are utilized for close tube spacing for optimum heat transfer performance of
the core, although other tube shapes and cross-sections may be utilized. The
30 present invention provides easy and inexpensive assembly through the use of
specifically configured grommets which do not rely on compression of the
grommet between the tube and the inside of the header hole for sealing. This
reduces the force required for assembly and requirements for close part tolerance.
The design of the grommets as described herein simplifies insertion of the
35 gron,ri,els into the header and further facilitates unit assembly. The present
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invention also co,-terl,plates an improved header configuration and an improved
fin configuration in the area of the core adjacent to the header.
The preferred grommet of the present invention is depicted in its unstressed
or undeformed condition in Fig. 5. Grommet 50 is preferably made of a silicone
5 rubber or other resilient, flexible or compliant polymer or other material which
provides good sealing against the other components of the heat exchanger which
are typically made of a metal or alloy. Grommet 50 comprises a body portion
having an opening therein to receive the tube from a heat exchanger core. A
radially outwardly extending lip or flange 58 is disposed at a first, upper end of the
10 body portion and a radially inwardly extending lip or flange 60 is disposed at a
second, lower end of the grommet. It should be understood that relative
directional terms are used herein for reference only in connection with the
drawings and the grommet and other components may be utilized in any position
other than that shown. Outward lip 58 has an angular portion 62 extending down
15 and inward to the outer wall section 54 of the grommet, which extends straight
downward from there to the lower end of the grommet. Inner wall 56 extends
straight downward from the upper end of the grommet until it reaches radially
inwardly projecting lip 60. As seen in the axial cross-section shown in Fig. 5, both
upper and lower lips 58 and 60 have generally rounded corners. However, any
20 other shape or configuration of these lips may be utilized. Also, the body portion
of grommet 50 may be conical in shape.
As shown in Figs. 8 and 9, grommet 50 has a configuration which conforms
to the shape of the oval openings 52 in header plate 28 which are sized to receive
tubes 22 from the header core (see Fig.10). Header 28 has an opening 52 for each25 tube which is to be connected to the header/tank assembly. As used herein theterm "oval" refers to any non~ircular shaped axial cross-section (i.e. perpendicular
to the axis of the tube) having a generally smoothly curving periphery, such as an
ellipse or a rectangle with rounded corners, or other obround or egg shape. 8eing
of oval cross-sectional shape, such tubes and openings will have a diameter in one
30 direction Breater than the diameter in another (usually perpendicular) direction,
which are referred to herein as the "major diameter" and "minor diameter"
respectively. While oval shaped tubes and, consequently, oval shaped header
openings and grommets are preferred, other tube, opening and grommet
configurations can be used, such as circular or rectangular.
21fi7~42
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Fig. 6 shows the insertion of grommet 50 into header 28 and the beginning
of insertion of lower end 48 of tube 22 into the grommet in the direction indicated
by the arrow. Header opening 52 is provided with generally the same
configuration as the cross-section of tube end 48, although the header opening is
5 larger in dimension (both major diameter and minor diameter). The unstressed
diameter "d" of grommet 50 (Fig. 5) is substantially the same as, or less than the
diameter of header opening 52. This ensures that the grommet 50, when inserted
into the header 52 openings as shown in Fig. 6, is substantially undistorted. During
assembly, it is preferred that grommet 50 is inserted first into header opening 52.
10 Following that, tube 22 is inserted into the grommet. Since the upper lip or flange
58 is the only portion of the grommet extending radially outwardly from the body,
insertion from one side of the header is facilitated. Preferably, the grommet isinserted from the so-called "air" side 27 of the header, i.e., the portion of the
header which is exposed to surrounding atmosphere external to the heat
15 exchanger. The lower end of the grommet having the inwardly projected end is
inserted into the header opening first and, after insertion, extends from the so-
called "fluid" side 29 of header 28, i.e., the side which is exposed to the air or
liquid inside the heat exchanger. After full insertion, outward lip 58 remains
external to header opening 52 and preferably contacts air side surface 27 of the20 header.
Since the inward extending lip 60 of grommet 50 has a diameter essentially
the same as or less than the outer diameter of tube end 48, upon full insertion of
the tube from the air side of the header through the grommet, contact will be made
between inward grommet lip 60 and the outside surface of tube end 48 (Fig. 7).
25 The unstressed inner diameter of the body portion of grommet 50 is preferablygreater than the outer diameter of tube end 48 over the major portion of the
~on.r-,et height. This provides for easy entry and lead-in of the tube into the
grommet and, after full entry, will provide a gap between a substantial portion of
the outer surface of the tube end 48 and the inner diameter of the grommet 50
30 body portion within the header opening.
Preferably, the inner diameter of the inward lip 60 is less than the outer
diameter of tube end 48 so that, after full insertion of the tube as shown in Fig. 7,
the outer wall of the lower end of grommet 50 is forced radially outward. Because
of the resilience of the grommet material, the tube stretches the grommet in the35 lower region and flexes its walls to provide good sealing contact between the
216~642
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inward lip 60 and the outside surface of tube end 48 and form a tight seal around
the tube. Additionally, the expansion of inward lip 60 bulges or forces outward
grommet outer wall portion 54 which locks against and forms a seal with the edgeof header opening 52 to prevent the grommet from slipping back out of the header5 opening. Sealing of the grommet to the tube and the header is further enhanced by
the action of internal pressure inside the tank/header assembly which serves to
force the lip 60 radially inward into tighter contact with both the tube and theheader, in the manner of an O-ring seal.
Although a portion of the external surface of tube 22 within grommet 50 is
10 still spaced from, and does not contact, the inner wall 56 of the grommet, the
inside surface of the upper end 58 of the grommet may be also forced inward to
contact the tube outer surface to seal against leakage. Additionally, the lower
outside edge of outward lip 58 also may seal against the edge of the header
opening 52 to provide an additional seal.
Variations in grommet design may be employed, such as those shown in
Figs. 12 and 13. As shown in Fig. 12, the unstressed grommet 72 at the right,
without the tube inserted, has an outer surface 84 which curves inward near the
lower end before terminating in inward lip 80. Again, outer wall 84 fits snugly
against the header opening when the grommet is first inserted, but is not oversized
20 so as to distort the shape of the grommet. Upper outward lip or flange 76 also may
be rectangular in aoss-section, as shown. However, the same principle of
operation exists for the alternative grommet 72 configuration. As shown in the left
portion of Fig. 11, tube 22 is inserted through the body of the grommet so that
lower inward lip 80 seals against tube 22 and the grommet outer body portion is
25 thereby forced or stretched outward to lock and seal against the edge of the header
opening. There also remains a gap between a portion of the exterior wall of tube22 within the grommet and grommet inner wall 88.
Fig. 13 again shows another alternative embodiment 74 of the grommet of
the present invention. In this embodiment, the principal difference with previously
30 described grommet 50 is that lower inward lip 82 also includes an outwardly
extending portion to enhance the ability of the grommet to lock into the edge ofheader 28 opening when the tube 22 is inserted through the body of the grommet.
The result of the invention remains the same, that is, the sealing without
compression of the grommet between the tube and header which permits greater
35 tolerances in the location of tubes vs. header holes.
21676 12
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Thus, in summary, assembly of the heat exchanger utilizing the grommet
configuration of the present invention may commence by inserting the grommet
into the header, the header being optionally joined or formed to the tank in a prior
step by any conventional method known in the art. Following insertion of the
5 grommets into the header openings, preferably from the air side of the header, the
tubes for the heat exchanger core are then inserted from the same side as the
grommet was inserted. The tubes may be inserted individually, one at a time, or
preferably may be inserted simultaneously because of the low assembly force
required as a result of the grommet configuration. Subsequently, the core may be10 connected to the tanks to complete the heat exchanger assembly.
The present invention also contemplates the preferred use of serpentine fins
in the core, as shown in Fig. 14. Fins 70 are made of thin metal strip such as
copper, aluminum or brass having high thermal conductivity. These serpentine fins
70 are bent in a series of alternating bends so that the roots 92 of the bends contact
15 tubes 22. The fins are soldered or brazed to the tubes at these roots 92 to ensure
good thermal conductivity between the tube 22 and the fins 70. The portions of fin
70 between alternating roots 92 transfer the majority of the heat from the fluidinside the tube to the ambient air outside of the heat exchanger. Fins 70 continue
along tube 22 and terminate at the free end 93 of the strip near tube end 48.
In order to provide space for the header and lock grommets 50 within
header plate 28, the serpentine pattern of fin 70 is compressed near tube end 48prior to brazing or soldering the fins to the tubes in the manufacture of the heat
exchanger core. More preferably, the strip is also cut so that free ends 93 of
substantially all of fins 70 terminate at a position where a root would be, i.e.,
25 closely adjacent to or in contact with the tube outer surface, rather than at a point
somewhHe between the tubes. After assembly, this compression or "combing" of
the fins permits the tube ends 48 to extend a length "I" to provide a proper location
of the tubes into the tank/headH assembly and helps provide locking of the
grommet in place in the header openings. In this case, the compressed pattHn of
30 the fins 70 contacts and pushes against the top lip 58 portion of grommet ~0 to
hold it securely in place. Additionally, since the free end 93 of fin 70 is cut at the
root, instead of at random, this avoids the accidental introduction of portions of the
fins into the area between the grommet and the tube.
Turning back to Fig~ 10, it is seen that the width "w" of header plate 28 is
35 only slightly greater than the width of header openings 52 (and only slightly greater
2167S42
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than the major diameter of tube 22 shown in phantom line inserted into the header
opening). This minimizes header flexing and achieves maximum header strength.
Additionally, the header is preferably made with a relatively flat or planar central
section which contains the openings for the tube ends. As shown in Fig. 11, on
5 opposite sides of the header central section are flanges 64, 66 extending
approximately 90 degrees from the plane of the central section. Since the entireheader is prefHably made of a single stamped or formed metal strip, the thickness
of the header central portion and flanges is generally uniform throughout. The free
ends of flanges 64, 66 (the ends most distant from the header central section) may
10 be attached by welding or other means to the tank (Fig. 15). The height "h" of
flanges 64, 66 are such that, when the distant end of the header flange is welded to
the tank, the strength of the area of connection between the flanges and the header
central portion is unaffected by heat generated during the welding. Preferably
flange height h is at least about 2.5 cm.
It has also been found that, as a result of the operation of welding the header
28 to the tank of the heat exchanger, the length "a" of the header shrinks.
Consequently, the present invention also provides that the header length "a", along
with the spacing of the header openings, be initially fabricated to be greater than
the spacing between the tubes extending from the completed heat exchanger core.
20 For example, an additional initial length of 0.003 inches per foot (0.25 mm/m) of
header length has been found to be desirable. As the header is welded to the tank,
it shrinks the length of the header so that the spacing between the header openings
is reduced to conform to the spacing of the tube ends.
As shown in Fig. 15, header 28 is assembled to the conforming opening in
25 the side of tank 100, preferably by welding as previously described. An additional
tank opening 102 is provided as either an inlet or an outlet for the completed tank
and header assembly. The grommets 50 may be inserted into the header openings
52 after welding of the header to the tank. Preferably the individual grommets are
connected by a web 68 made out of the same resilient material as the grommets
30 themse1ves.
After assembly of the tank, header and grommets, the entire heat exchanger
is assembled. As shown in Fig. 16, heat exchanger 110 comprises the core 94
which has structural core extensions 96 on the upper and lower sides thereof.
These core extensions have overhanging ends which mate with corresponding
35 portions of the tank. The tube ends are aligned with and partially inserted into the
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corresponding grommet openings in the headers, and an entire
tank/header/grommet assembly is then pushed onto the core at either end. A
mechanical fastener 104a, 104b is provided to connect the tanks 100a, 100b on
either end of core 94. This mechanical fastener is provided so that the tanks may
5 be easily disassembled from the core for servicing. Any type of mechanical fastener
may be utilized, such as a bolt or snap-type fitting. Preferably, a snap-on
arrangement is preferred which uses a ramped protrusion extending from the tankswhich snaps into corresponding openings in the ends of support member 96.
To assemble the heat exchanger, preferably the header is first assembled to
10 the tank in the manner described above. The resilient grommet is inserted into the
opening in the header with the inwardly extending lip end first. The tube or
assembly of tubes is then inserted into the header opening through the grommet
body such that the inwardly extending lip connects the tube to form a sealed tube-
to-header joint.
In accordance with the present invention, accurate positioning of the tubes
with respect to the header holes is not critical since the configuration is not
dependent on precise compression of the grommet between the tube and the inside
of the header hole for sealing. The mechanical assembly of the joint between theheader and tubes and between the core and tanks permits easy disassembly of the
20 unit for replacement of the core in the event of damage in the field. The
mechanical joint is possible only because of resilient tube-to-header joints which
minimize tube-to-headH stresses due to thermal expansion and result in very low
stress in the joints between the structural pieces and the tanks. Additionally, the
eventual assembly of the charge air cooler or other heat exchanger into the vehicle
25 where it is attached to other structure provides sufficient additional mechanical
support so that welding of the side supports is unnecessary.
This invention provides a heat exchanger such as a charge air cooler with
greatly reduced stresses on the tube-to-header joint caused by thermal expansion of
the tubes and tank internal pressure. Tests have shown that such a design will have
30 a life of up to ten times greater than that of a conventional brazed joint charge air
cooler. For example, typical brazed joint charge air coolers develop small leaks in
the tube-to-header joint after only 1,000 cycles of thermal cycle testing and fail
completely due to major leaks after 3,000 to 4,000 cycles. Charge air coolers with
resilient grommet tube-to-header joints made have survived 10,000 cycles without35 leaking.
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The invention also provides resilient grommet tube-to-header joints without
the need for compressing the rubber of the grommet between the tube and the
inside of the header hole. This eliminates the high forces required for compression
of the rubber during insertion of the assembly of tubes into the grommet. This
5 invention further provides for greater tolerances in the location of the tubes with
respect to the header holes than current designs and lowers manufacturing costs
because the design is not dependent for sealing on compression of the grommet
rubber the tubes and the insides of the header holes. This invention also provides
for use of oval tubes, grommets and header holes thus allowing closer spacing of10 the core tubes compared to using round tubes, grommets and headér holes. Thiscloser tube spacing in the core will provide optimum heat transfer performance.
While the ~.resent invention has been particularly desaibed, in conjunction
with a specific preferred embodiment, it is evident that many alternatives,
modifications and variations will be apparent to those skilled in the art in light of
15 the foregoing desaiption. It is therefore contemplated that the appended claims
will embrace any such alternatives, modifications and variations as falling within
the true scope and spirit of the present invention.
