Metal working – Method of mechanical manufacture – Process for making bearing or component thereof
Reexamination Certificate
2000-10-19
2001-12-18
Hughes, S. Thomas (Department: 3726)
Metal working
Method of mechanical manufacture
Process for making bearing or component thereof
C029S890127, C165S173000
Reexamination Certificate
active
06330747
ABSTRACT:
DESCRIPTION
1. Technical Field
This invention relates to heat exchangers and, more particularly, to motor vehicle heat exchangers utilizing grommets in the tube-to-header joints.
2. Background Art
Heat exchangers, particularly those utilized in motor vehicles, may be liquid-to-air heat exchangers, (e.g., radiators for engine coolant, air conditioning condensers and evaporators, and oil coolers) or may be air-to-air heat exchangers (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 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 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 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 is generally secured by brazing or soldering to the tube. A strip portion between he 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.
Headers
28
a
and
28
b
are at the top and bottom, respectively, of core
20
and are plates having openings therein to receive and seal the upper and lower ends of the tubes
22
. Upper and lower tanks
34
a
and
34
b
, respectively, are normally welded or soldered to headers
28
a
and
28
b
respectively and contain an inlet
36
and 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 oval with circular ends. Prior art methods of welding tube-to-header joints are disclosed, for 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 manifolds are fixed with respect to each other by the unit framework or structure, the growth 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, creating further stresses on the tube-to-header joints. The combination of stress resulting from thermal expansion and 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 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 strength.
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
. Metallic headers
28
are mechanically attached to tanks (not shown), such as by bolting, 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 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 extremely effective 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 header, and also provided a gasket for sealing the headers to the 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 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.
Other radiators have also utilized rubber grommets in their tube-to-header joints. These radiators have been designed around individual finned tubes having round ends and oval cross-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 thereby avoiding high assembly forces. This allowed the construction of very large radiators for heavy construction equipment. However, it has been found that the use of tubes with round ends limits this design to cores having rather wide tube spacing which results in relatively poor thermal performance compared to most radiator core designs.
U.S. Pat. Nos. 4,756,361 and 5,205,354 describe a radiator which utilizes tubes which are circular in cross-section throughout their length. This type of design is shown in
FIG. 4
in which tubes
22
are pressed through collar openings
25
in flat 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 on the top and bottom of the header plate. Because of its round tubes, this design also suffers from poor thermal performance compared to most radiator designs and must have close tolerances to achieve the required compression of the grommet between the tube and header opening
Kolb Michael J.
Lambert Marco
Butler Mark A.
DeLio & Peterson LLC
Hughes S. Thomas
Transpro, Inc.
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