U.S. patent application number 12/616321 was filed with the patent office on 2011-05-12 for apparatus for maintaining a urea solution in a liquid state for treatment of diesel exhaust.
Invention is credited to Daniel B. Hamilton, Bob X. Li, Michael J. Seino.
Application Number | 20110107744 12/616321 |
Document ID | / |
Family ID | 43558038 |
Filed Date | 2011-05-12 |
United States Patent
Application |
20110107744 |
Kind Code |
A1 |
Seino; Michael J. ; et
al. |
May 12, 2011 |
Apparatus for Maintaining a Urea Solution in a Liquid State for
Treatment of Diesel Exhaust
Abstract
A system for keeping a reservoir solution of urea in a liquid
state at normally sub-freezing temperatures comprising a reservoir
tank module having a heater and disposed in a solution storage
tank. Solution in the storage tank is heated by passage of heat
through the walls of the reservoir tank module which are formed of
a hybrid of plastic polymer and metal, preferably a urea-resistant
stainless steel, such that the thermal conductivity of the walls is
sufficient to liquefy frozen solution in the storage tank in a
practical time frame at an acceptable net manufacturing cost for
the tank module. The hybrid combination may be formed in any of
various arrangements such as, but not limited to, a lower portion
formed of metal and an upper portion formed of plastic, or
alternating bands and/or strips of metal and plastic. The optimum
thicknesses of metal and plastic may be determined
conventionally.
Inventors: |
Seino; Michael J.;
(Flushing, MI) ; Li; Bob X.; (Flint, MI) ;
Hamilton; Daniel B.; (Grand Blanc, MI) |
Family ID: |
43558038 |
Appl. No.: |
12/616321 |
Filed: |
November 11, 2009 |
Current U.S.
Class: |
60/295 ;
220/592.2 |
Current CPC
Class: |
F01N 2610/10 20130101;
Y02T 10/12 20130101; F01N 2610/1406 20130101; Y02T 10/24 20130101;
F01N 2610/02 20130101; F01N 3/2066 20130101 |
Class at
Publication: |
60/295 ;
220/592.2 |
International
Class: |
F01N 13/14 20100101
F01N013/14; B65D 81/38 20060101 B65D081/38 |
Claims
1. A reservoir tank module for a system for keeping a reservoir
solution of urea in a liquid state at normally sub-freezing
temperatures, comprising hybrid walls formed of metal and plastic
polymer.
2. A reservoir tank module in accordance with claim 1 wherein said
metal is formed as a pot-shaped portion and said plastic polymer is
formed as a portion joined to said pot-shaped portion.
3. A reservoir tank module in accordance with claim 2 wherein said
joining of said pot-shaped portion to said cylindrical portion
includes respective mating barbed portions.
4. A reservoir tank module in accordance with claim 1 wherein said
metal is formed as a plurality of strips and said plastic polymer
is formed as a matrix encompassing said plurality of metal
strips.
5. A reservoir tank module in accordance with claim 4 wherein at
least two of said plurality of strips are interconnected.
6. A reservoir tank module in accordance with claim 1 wherein said
metal is formed as a plurality of bands and said plastic polymer is
formed as a matrix encompassing said plurality of metal bands.
7. A reservoir tank module in accordance with claim 6 wherein at
least two of said plurality of bands are interconnected.
8. A reservoir tank module in accordance with claim 1 further
comprising a heater.
9. A reservoir tank module in accordance with claim 8 wherein said
heater in contact with said hybrid walls formed of metal.
10. A system for keeping a reservoir solution of urea in a liquid
state at normally sub-freezing temperatures, comprising: a) a
storage tank for said urea solution; b) a reservoir tank module in
hydraulic communication with said storage tank for dispensing said
urea solution, wherein said reservoir tank module includes hybrid
walls formed of metal and plastic polymer.
11. A system in accordance with claim 10 wherein said reservoir
tank module is disposed within said storage tank.
12. A system in accordance with claim 10 wherein said hybrid walls
comprise metal formed as a pot-shaped portion and plastic polymer
formed as a portion joined to said pot-shaped portion.
13. A system in accordance with claim 10 wherein said hybrid walls
comprise metal formed as a plurality of strips and plastic polymer
formed as a matrix encompassing said plurality of metal strips.
14. A system in accordance with claim 10 wherein said hybrid walls
comprise metal formed as a plurality of bands and plastic polymer
formed as a matrix encompassing said plurality of metal bands.
15. An internal combustion engine comprising a system for keeping a
reservoir solution of urea in a liquid state at normally
sub-freezing temperatures, wherein said system includes a reservoir
tank module having hybrid walls formed of metal and plastic
polymer.
16. An engine in accordance with claim 15 wherein said engine is
compression-ignited.
17. An engine in accordance with claim 15 wherein said engine is
lean burn spark ignited.
Description
TECHNICAL FIELD
[0001] The present invention relates to emissions control in
compression-ignited and lean burn spark ignition internal
combustion engines; more particularly, to systems for injecting
urea into the engine exhaust to scavenge nitrogen oxides; and most
particularly, to a system for liquefying a storage tank solution of
urea at normally sub-freezing urea-solution temperatures.
BACKGROUND OF THE INVENTION
[0002] To scavenge oxides of nitrogen (NOx) from the exhaust of an
internal combustion engine, such as for example, a
compression-ignited (Cl) diesel engine, urea injection systems are
commonly in use in the prior art. An aqueous urea solution is
injected into the hot exhaust pipe, where urea is hydrolyzed into
ammonia ahead of a selective catalytic reduction (SCR) converter.
Ammonia reacts with NOx trapped on the catalyst face to form
N.sub.2, CO.sub.2, and H.sub.2O, thereby lowering the level of
noxious emissions in the exhaust.
[0003] A serious problem in the prior art is that at temperatures
below about -11.degree. C., the urea solution can freeze. Thus, a
thermal heating system and method are required to thaw the solid
solution into a liquid solution (or to keep the solution from
freezing) to permit a pump to draw solution for delivery into the
exhaust pipe.
[0004] A typical prior art urea supply system comprises a
relatively small reservoir tank module from which liquid urea
solution is dispensed into a diesel engine exhaust system, and a
larger storage tank in which the tank module is immersed. The tank
module contains a resistance heater that can liquefy suitable
quantities of solution in a short time, as is required to meet
government air pollution standards. Solution in the storage tank is
heated by transfer of heat through the walls of the heated tank
module. It is an important operating requirement that the storage
tank be able to re-supply the tank module within a short time after
starting of the engine.
[0005] In prior art systems when the solution in the storage tank
is frozen, meeting this requirement can be difficult because of
limited heat flow through walls of the tank module, which typically
is formed of a plastic polymer having relatively low thermal
conductivity. It is known to have substituted an all-metal tank
module, which has satisfactory thermal conductivity, but the
corrosive nature of a urea solution dictates forming the tank
module of urea-resistant stainless steel, making this approach
cost-prohibitive.
[0006] What is needed in the art is an improved reservoir tank
module having thermal conductivity sufficient to liquefy frozen
urea solution in a practical time frame and having an acceptable
net manufacturing cost.
[0007] It is a principal object of the present invention to provide
a reliable flow of liquid urea solution at ambient temperatures
below the freezing point of the solution at an acceptable net
manufacturing cost of a urea supply system.
SUMMARY OF THE INVENTION
[0008] Briefly described, a system for keeping a reservoir solution
of urea in a liquid state at normally sub-freezing temperatures
comprises a reservoir tank module disposed in a storage tank. The
reservoir tank module preferably includes a level sensing
apparatus, inlet and outlet ports for supplying and withdrawing
urea solution, and at least one heating element. The walls of the
reservoir tank module are preferably immersed in urea solution
contained in the storage tank, which solution is heated by passage
of heat through the walls of the reservoir tank module.
[0009] In accordance with the present invention, the walls of the
reservoir tank module are formed of a hybrid of plastic polymer and
metal, preferably a urea-resistant stainless steel, such that the
thermal conductivity of the walls is sufficient to liquefy frozen
urea solution in the storage tank in a practical time frame and at
an acceptable net manufacturing cost for the reservoir tank
module.
[0010] The hybrid combination may be formed in any of various
arrangements such as, but not limited to, a lower portion formed of
metal and an upper portion formed of plastic; and a pattern of
alternating bands and/or strips of metal and plastic. The metal may
be exposed to solution within the reservoir tank module and/or the
storage tank; or the metal may be shielded by plastic at either or
both locations. The reservoir tank module may be formed by any
convenient forming process such as, but not limited to, forming of
the metal components as by stamping from sheet stock of powdered
metal casting followed by joining or overmolding of the plastic
components onto the metal components. For any given application,
dependent in part upon the expected climatic extremes during use
and the costs of materials, the optimum thermal transfer areas and
thicknesses of metal and plastic may be determined conventionally
as by computer modeling and/or simple experimentation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The present invention will now be described, by way of
example, with reference to the accompanying drawings, in which:
[0012] FIG. 1 is an elevational schematic view of a prior art
system for keeping a reservoir solution of urea in a liquid state
at normally sub-freezing temperatures;
[0013] FIG. 2 is an elevational view of a first embodiment of a
hybrid reservoir tank module in accordance with the present
invention showing metal and plastic portions of the hybrid
tank;
[0014] FIG. 3 is an enlarged cross-sectional view of a preferred
arrangement for joining the metal and plastic portions shown in
FIG. 2;
[0015] FIG. 4 is an elevational view of a second embodiment of a
hybrid reservoir tank module; and
[0016] FIG. 5 is an elevational view of a third embodiment of a
hybrid reservoir tank module.
[0017] The exemplifications set out herein illustrate
currently-preferred embodiments of the present invention, and such
exemplifications are not to be construed as limiting the scope of
the invention in any manner.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] Referring to FIG. 1, a portion of an exemplary prior art
system 10 for supplying a solution of urea to an exhaust emissions
control system 12 such as, for example, a compression-ignited
diesel engine or a lean burn spark ignition engine 14 comprises a
reservoir tank module 16 disposed within a storage tank 18 for urea
solution 20. Solution 20 enters tank module 16 via an inlet 22 and
is dispensed via an outlet 24. A heater 26 is disposed within tank
module 16 for liquefying solution 20 within module 16. Excess heat
from heater 26 is intended to pass through the walls 28 of tank
module 16 and locally liquefy solution 20 in proximity to tank
module 16 and inlet 22 to allow gravitational replenishment of
solution into tank module 16. As described above, a problem exists
in operation of prior art systems 10 in that walls 28 of reservoir
tank module 16 are typically formed of a plastic polymer having
relatively low thermal conductivity such that at extreme low
temperature conditions insufficient heat is passed into storage
tank 18 to maintain an adequate rate of liquefaction and
replenishment.
[0019] Referring to FIGS. 2 and 3, a first embodiment 116 of an
improved hybrid reservoir tank module, for substitution for prior
art reservoir tank module 16 in system 10 to form an improved
system 110, comprises a pot shaped lower portion 140 formed of a
urea-resistant metal such as stainless steel and an upper portion
142, which may be cylindrical, formed of a plastic polymer and
joined to lower portion 140 at juncture 144. The joining may be
effected by any desired process for joining metal to plastic,
although in a currently preferred embodiment the mating portions
140,142 of embodiment 116 are provided with respective matable
barbed portions 146,148 as shown in FIG. 3 which are formed around
the peripheries of the respective portions and which are engaged by
urging portions 140,142 together. The relative size and thickness
of portions 140,142 may be determined conventionally as by computer
modeling and/or simple experimentation.
[0020] Referring now to FIG. 4, a second embodiment 216 of an
improved hybrid reservoir tank module, for substitution for prior
art reservoir tank module 16 in system 10 to form an improved
system 210, comprises walls 228 formed of a plurality of
urea-resistant interconnected metal strips 240 such as stainless
steel embedded in an interlocking plastic matrix 242 formed of a
plastic polymer as by overmolding in known fashion. Strips 240 may
be exposed on the inner and/or outer surfaces thereof or may be
covered with plastic 242 on either or both surfaces. The material
choice for the strips is made to optimize heat transfer and urea
solution compatibility. The relative size and thickness of portions
240,242 may be determined conventionally as by computer modeling
and/or simple experimentation.
[0021] Referring now to FIG. 5, a third embodiment 316 of an
improved hybrid reservoir tank module, for substitution for prior
art reservoir tank module 16 in system 10 to form an improved
system 310, comprises walls 328 formed of a plurality of
urea-resistant interconnected metal rings or bands 340 such as
stainless steel embedded in an interlocking plastic matrix 342
formed of a plastic polymer as by overmolding in known fashion.
Strips 340 may be exposed on the inner and/or outer surfaces
thereof or may be covered with plastic 342 on either or both
surfaces. Strips 340 may be continuous around the periphery of
module 316 or may be discontinuous as shown in FIG. 5. The relative
size and thickness of portions 340,342 may be determined
conventionally as by computer modeling and/or simple
experimentation.
[0022] In each embodiment shown in FIGS. 2,4 and 5, the heater
element 26 may be disposed in contact with the metal
portion/strips/bands 140,240,340 for improved heat transfer.
[0023] While the invention has been described by reference to a
specific embodiment, it should be understood that numerous changes
may be made within the spirit and scope of the inventive concepts
described. Accordingly, it is intended that the invention not be
limited to the described embodiment, but will have full scope
defined by the language of the following claims.
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