Abstrict A condenser (10) with a return header tank (14) has a receiver
tank (22) physically attached along side a return header tank (14).
The bottom of receiver tank (22) is closed by an end cap (42) that
is attached during the single, high temperature braze process that
forms the entire condenser. The desiccant cartridge assembly (24)
of the invention has components of a material and design that allow
it to be installed within tank (22) before the end cap (42) is attached
during the braze process, with no subsequent steps.
Claims 4. A condenser having a header tank and a receiver tank attached
to said header tank, said receiver tank having a tubular body, an
end closure brazed to one end thereof and an end closure brazed
to an opposite end thereof, said condenser further comprising a
desiccant cartridge assembly installed within the receiver tank
prior to a brazing operation for brazing the end closures to the
tubular structure, said desiccant cartridge assembly comprising,
a tube formed of a material capable of withstanding the braze operation,
and inserted within the receiver tank spaced apart by a radial clearance,
said tube comprising an open end, a desiccant material contained
with the tube spaced apart from the open end and exposed to refrigerant
within said receiver tank, a filter plug formed of a material capable
of withstanding the brazing operation, said filter plug being disposed
within the tube adjacent the open end to retain said desiccant material,
and, a locating and retention member between the tube and the tubular
body of the receiver tank so as to maintain said tube radially centered
and axially retained.
5. A condenser according to claim 1 further characterized in that
said locating and retention member is a clip formed of a braze compatible
material that brazes to the outside of said tube and to the inside
of said tubular body.
6. A condenser according to claim 1 further characterized in that
the filter plug has a porosity sufficiently small to retain said
desiccant material and sufficiently large to admit refrigerant,
said desiccant cartridge assembly further comprising a screen disposed
within the open end of the tube and retaining the filter plug.
Description TECHNICAL FIELD
[0001] This invention relates to condensers with integrated receivers,
and specifically to a desiccant cartridge capable of being installed
in the receiver prior to the condenser brazing operation.
BACKGROUND OF THE INVENTION
[0002] Certain automotive air conditioning systems use a canister
like reservoir container for refrigerant located downstream of the
condenser, generally referred to as a "receiver." This,
as opposed to a reservoir canister located upstream of the compressor,
generally called an accumulator. Historically, receivers have been
separate canisters plumbed into the system at a location remote
from the condenser, but lately, many designs have been proposed
for directly structurally integrating the receiver/reservoir with
the outlet manifold tank of the condenser itself, often by co extruding
the two, or brazing them directly together when the entire condenser
is brazed. This generally creates a long, thin reservoir tank, directly
adjacent to the outlet manifold tank of the condenser.
[0003] An air conditioning system needs a supply of desiccant to
which the refrigerant charge is continually exposed during the life
of the system in order to pick up any traces of moisture entering
the lines. The refrigerant reservoir canisters have generally been
the most convenient location for the desiccant supply, which may
be in a filter bag or cartridge somehow fixed inside the canister
before it is closed up. Whatever the location, it is necessary that
the desiccant material be well exposed to the refrigerant flow,
but be protected from jostling, fracture or dislodgment, so as to
prevent any of the desiccant particles from migrating through the
lines and doing damage to other parts of the system.
[0004] In the case of condensers with integral receivers, often
referred to as integral RD's, existing patents show a number of
variations on a common theme. Various cartridges and other assemblies
are provided to allow the desiccant charge to be installed after
the basic condenser/receiver structure has been run through the
braze oven and substantially completed, but for the addition of
one or more end caps to the integral receiver tank itself. The desiccant
assembly is generally made long and thin so as to take maximum advantage
of the interior size of the receiver tank while still allowing the
refrigerant to rise and fall freely within. The cartridge is axially
inserted post braze, and the tank end cap added last. The end cap
may be threaded and removable, or welded in place. In either case,
the desiccant assembly or cartridge need not tolerate any more heat
than, at the most, the heat involved in brazing on the end cap itself,
which is localized and rather brief. For example, co owned U.S.
Pat. No. 6170287 shows a long, thin fabric sleeve held above and
away from the end cap by a plastic post or stand off, which protects
the sleeve from the heat of end cap welding, and later maintains
the sleeve axially, and, to an extent, radially in position during
condenser operation. None of these known assemblies, however, would
allow the desiccant cartridge to be installed before the condenser/receiver
assembly was brazed, which involves temperatures approaching 1200
degrees F. for substantially longer periods than it takes to weld
on an end cap. Consequently, a post braze installation operation
is a necessity, which adds cost and cycle time.
SUMMARY OF THE INVENTION
[0005] The invention discloses a desiccant cartridge structure
for a condenser with integrally brazed receiver tank that allows
the cartridge to be assembled and installed before the condenser
braze operation. In the embodiment disclosed, the cartridge is also
fixed in place within the tank by and during the braze operation
itself.
[0006] In the preferred embodiment, all parts of the desiccant
assembly or cartridge are initially chosen to be capable of withstanding
the braze operation temperature. These components include a long,
thin heat resistant tube (preferably, a metal tube of material similar
to the tank itself), filled with a heat resistant desiccant and
open to refrigerant flow through a suitable heat resistant filter
material and ventilated end closure. A similarly heat resistant
locating and retention member serves to keep the cartridge axially
and radially located within the tank interior as it is inserted
within the tank, prior to the tank being closed with its end cap.
The tank end cap is fixed to the tank by and during the braze operation,
with no post braze operation needed, and the desiccant cartridge
remains in place, without damage, during the same braze operation.
In the embodiment disclosed, the locating and retention member is
a crown shaped clip surrounding the cartridge tube, which not only
withstands the braze operation, but takes advantage of it by fusing
to the tube and tank interior so as to fix it permanently within
the tank.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] These and other features of the invention will appear from
the following written description, and from the drawings, in which:
[0008] FIG. 1 is a schematic view of the general type of condenser
and integrated receiver tank referred to above;
[0009] FIG. 2 is a perspective view of the components of the desiccant
cartridge disassembled;
[0010] FIG. 3 is a plan view of the completed cartridge;
[0011] FIG. 4 is a cross section taken along the line 4-4 of FIG.
3;
[0012] FIG. 5 shows the cartridge about to be inserted into the
receiver tank, prior to the braze operation;
[0013] FIG. 6 shows the cartridge fully inserted, with the end
cap being added;
[0014] FIG. 7 shows the cartridge being brazed in place inside
the tank during the basic condenser brazing operation itself.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0015] Referring first to FIG. 1 a condenser 10 of the cross flow,
headered type, or brazed aluminum construction. Condenser 10 has
an inlet/outlet header tank 12 on one side, and a return header
tank 14 on the other, each of which is divided into discrete upper
(U) and lower (L) sections by separators 16 and 18 respectively.
Heated, compressed refrigerant vapor enters the upper section (U)
of header tank 12 above separator 16 and flows across and through
the flow tubes in the main pass section (not illustrated in detail).
In the main pass, refrigerant is condensed to liquid form and flows
into the upper section (U) of return tank 14 above the separator
18. From there, all liquid refrigerant is forced, by the separator
18 to flow through an upper inlet 20 and into an attached reservoir
or receiver tank 22 where it backs up into a reserve column of
varying height. From the reserve column, liquid refrigerant can
flow down and through a lower outlet 21 into lower section (L)
of return tank (14) and ultimately into a sub cooler section of
condenser 10 comprised of those flow tubes located below the two
separators 16 and 18. In the sub cooler section, liquid refrigerant
is further cooled, below the temperature necessary to simply condense
it, and flows finally back into the lower section (L) of header
tank 12. The desiccant containing structure of the invention, not
illustrated in FIG. 1 is installed within receiver tank 22 as
described next. Mutually contacting surfaces of the various components
of condenser 10 (tube ends to tube slots, fin surface to tube outer
surface, etc) are, as is conventional, clad with a braze material
of a eutectic aluminum-silicon alloy that melts at braze temperatures,
is pulled by capillary action into contact interfaces, and later
hardens to form structural and sealed joints.
[0016] Referring next to FIGS. 2 through 4 a preferred embodiment
of the desiccant cartridge of the invention, referred to generally
at 24 is illustrated. Cartridge assembly 24 has relatively few
components, the materials for which are chosen primarily so as to
be capable of withstanding the typical temperatures and times of
the braze process, which can rise to around 1200 degrees F. The
main component is a long, thin cylindrical tube 26 of aluminum
or other material that is heat resistant and compatible with the
base material of receiver tank 22. As disclosed, tube 26 is substantially
closed at the upper end and, initially, open at the lower end, with
a wall thickness of approximately half a millimeter, and approximately
250 mm in length and 25 mm in diameter, so as to take maximum advantage
of the axial and radial space within receiver tank 22. Tube 26 has
a volume sufficient to hold a charge of approximately 70 grams of
a suitable desiccant material 28 which, here, is a synthetic, crystalline,
potassium sodium alumina silicate molecular sieve, often referred
to simply as a synthetic zeolite. This material is suitable to the
product and process disclosed in that it absorbs moisture, and also
can withstand the braze temperatures described above. The desiccant
material 28 is packed into the tube 26 followed by a firmly packed
filter plug 30 about 25 mm thick, of a binderless felt material
of the general type manufactured by Johns Mansville Co., and referred
to as Micro-fiber Felt-Type E. The filter material is suitable to
the task by virtue of being, again, heat resistant, and also being
fine enough to retain the desiccant particles, but still porous
enough to freely admit refrigerant in and out. The filter plug 30
is followed by a disk shaped aluminum screen 32 which is pressed
down firmly against the filter plug 30 and then crimped in place
by the bottom edge of tube 26 being formed over its outer edge.
If desired, a bleed hole 34 can be added at the top of tube 26.
[0017] Still referring to FIGS. 4 through 6 the sub assembly of
tube 26 along with desiccant 28 filter plug 30 and retention screen
32 is positioned within the receiver tank 22 before and during the
braze process, as well as retained within receiver tank 22 thereafter,
by a locating and retention member in the form of a crown shaped
clip, indicated generally at 36. Clip 36 is also formed of a metal
compatible with the receiver tank 22 with a rim 38 that fits tightly
over the outside of tube 26 and a series of resilient, outwardly
extending fingers 40 sized to slide along and tightly, resiliently
engage the inner surface of tank 22 when inserted, as shown in FIG.
6. Clip 36 locates the entire desiccant assembly 24 axially above
the ports 20 and 21 as well as radially centered within the inner
surface of tank 22 with approximately 3 mm radial clearance all
the way around. As such, tube 26 takes maximum advantage of the
interior space within tank 22 but without blocking refrigerant
flow in any direction, and without blocking the inlet and outlet
20 and 21. Clip 36 is also clad, on both surfaces, with the same
kind of braze material referred to above.
[0018] Referring finally to FIGS. 6 and 7 after assembly 24 is
installed, a close fitting tank bottom end cap 42 is installed (but
not otherwise attached to tank 22) and the entire assembly of condenser
10 integral tank 22 and desiccant assembly 24 is fixtured and sent
through a braze oven, indicated schematically at 44. Within oven
44 all parts are heated to the braze melt temperature (higher than
the clad melt temperature, but significantly lower than the melt
temperatures of the base components themselves). The mechanical
retention force of the tight fitting clip fingers 40 within tank
22 is sufficient to keep tube 26 in place during the braze process,
during which time liquid braze material runs into the interface
between clip rim 38 and the outside of tube 26 as well as the interface
between the tips of clip fingers 40 and the inner surface of tank
22. Post braze, this solidifies to form a rigid joint between tube
26 and tank 22 just as at all other structural interfaces. As a
consequence of the structural connection formed during the basic
braze process, no post processing steps are needed either to install
the desiccant assembly or finish the receiver tank. Thus, the method
as disclosed does more than just tolerate or withstand the braze
process, it takes advantage of it, as well, to establish and create
a structural connection. In operation, rising refrigerant flows
up through screen 32 filter plug 30 and into and through the desiccant
charge 28 while any displaced gas exits the bleed hole 34 reversing
the process as it falls. The braze joints between clip 36 tube
26 and tank 22 are sufficient to hold up to vibration and jostling
during later operation of condenser 10 as much so as for any other
brazed joint in the entire structure. In addition, the resilience
of the clip fingers 40 helps to dampen such jostling, while the
radial clearance around tube 26 should prevent it from colliding
with the inside of tank 22.
[0019] Variations in the disclosed embodiment could be made. Any
heat resistant material for tube 26 could work, but the metal compatible
with the tank 22 is preferred, because it can work with the braze
process to establish structural joints, as noted. A tube 26 that
was very finely meshed or ventilated could, alone, serve to expose
the desiccant charge 28 to the refrigerant inside tank 22 while
still keeping the desiccant grains from sifting out. However, the
filter plug 30 and screen 32 would generally be more likely to assure
proper exposure and retention of the desiccant grains, especially
if they were likely to pulverize partially over long use. While
the structural use of the braze process is preferred, a clip like
36 could, for example, use barbs on the fingers 40 and a very tight
interference on the rim 38 so as grab the inner surface of the receiver
tank 22 and the outer surface of tube 26 respectively, and thereby
serve to adequately locate and retain the tube 26. Such a modified
clip would tolerate the braze process, and enable pre braze installation,
but without participating in the braze process per se. Such mechanical
force only installation would require a greater insertion force,
however. Theoretically, something comparable to the stand-off post
in U.S. Pat. No. 6170287 referred to above, if made of a heat
resistant material, and also designed to be fixed to the desiccant
tube 26 as well as to be fixable to the interior of tank 22 in such
a way as to radially and axially locate the tube 26 would work.
The clip 36 disclosed is smaller and lighter, however, and, since
it is fixable axially along the length of the tube 26 and radially
between outside of tube 26 and inside of tank 22 is much more efficient
at maintaining the axial and radial position of tube 26 both in
structural terms and in terms of low weight and material cost. |