U.S. patent application number 12/252184 was filed with the patent office on 2010-04-15 for optimized discrete level sensing system for vehicle reductant reservoir.
This patent application is currently assigned to FORD GLOBAL TECHNOLOGIES, LLC. Invention is credited to John Paul Bogema, Kevin Layden, Christopher Oberski, Furqan Zafar Shaikh, Michiel J. Van Nieuwstadt, Bret Alan Zimmerman.
Application Number | 20100089037 12/252184 |
Document ID | / |
Family ID | 42097640 |
Filed Date | 2010-04-15 |
United States Patent
Application |
20100089037 |
Kind Code |
A1 |
Bogema; John Paul ; et
al. |
April 15, 2010 |
OPTIMIZED DISCRETE LEVEL SENSING SYSTEM FOR VEHICLE REDUCTANT
RESERVOIR
Abstract
An example emissions-control system of a vehicle includes a
reservoir configured to contain a reductant solution, and an SCR
device disposed in the exhaust system and configured to consume the
reductant solution. The example emissions-control system further
includes a base sensor responsive to whether a volume of the
reductant solution exceeds a base volume, wherein the base volume
is a sum of a dead volume of the reservoir plus a standard volume,
and one or more elevated sensors corresponding to one or more
elevated volumes. The example emissions-control system further
includes an emissions sensor responsive to a NOX level in the
exhaust system, and a misformulation indicator operatively coupled
to the emissions sensor and to at least one of the base sensor and
an elevated sensor, and configured to indicate when an excess NOX
emission follows, within an interval, an increase in the volume of
the reductant solution above the base volume or an elevated volume.
The example emissions-control system may further include an
insufficiency indicator operatively coupled to the base volume
sensor and configured to indicate when the volume of the reductant
solution becomes less than the base volume.
Inventors: |
Bogema; John Paul; (Flat
Rock, MI) ; Zimmerman; Bret Alan; (Grosse Pointe
Farms, MI) ; Van Nieuwstadt; Michiel J.; (Ann Arbor,
MI) ; Oberski; Christopher; (Plymouth, MI) ;
Shaikh; Furqan Zafar; (Troy, MI) ; Layden; Kevin;
(Plymouth, MI) |
Correspondence
Address: |
ALLEMAN HALL MCCOY RUSSELL & TUTTLE, LLP
806 S.W. BROADWAY, SUITE 600
PORTLAND
OR
97205
US
|
Assignee: |
FORD GLOBAL TECHNOLOGIES,
LLC
Dearborn
MI
|
Family ID: |
42097640 |
Appl. No.: |
12/252184 |
Filed: |
October 15, 2008 |
Current U.S.
Class: |
60/286 ; 60/299;
73/114.75 |
Current CPC
Class: |
F01N 2900/1622 20130101;
F01N 2900/1814 20130101; F01N 2610/02 20130101; Y02A 50/20
20180101; F01N 3/208 20130101; Y02T 10/24 20130101; Y02T 10/12
20130101; F01N 3/2066 20130101; F01N 2610/1406 20130101; Y02A
50/2325 20180101 |
Class at
Publication: |
60/286 ;
73/114.75; 60/299 |
International
Class: |
F01N 3/20 20060101
F01N003/20; F01N 11/00 20060101 F01N011/00 |
Claims
1. A method of evaluating a reductant solution stored on-board a
vehicle in a reservoir, the vehicle having a reductant-delivery
system for delivering the reductant solution to an SCR device in an
exhaust system of the vehicle, the method comprising: varying a
reductant-solution delivery rate in response to a
reductant-solution concentration to maintain emissions-control
performance; distinguishing misformulation of the reductant
solution from other emissions-control system errors based on a
volume change in the reservoir in combination with an
emissions-control performance assay.
2. The method of claim 1, wherein the reductant-solution delivery
rate is varied among a plurality of rates, which include a nominal
rate and a maximum rate greater than the nominal rate.
3. The method of claim 2, wherein misformulation of the reductant
solution is indicated when an excess NOX emission occurs within an
interval following the volume change, the interval including a time
to deplete and refill a nominal operating amount of ammonia in the
SCR device.
4. The method of claim 2, wherein the volume change comprises an
increase in the volume of liquid in the reservoir above at least
one of a base volume and an elevated volume, where the base volume
is greater than a dead volume of the reservoir, and the elevated
volume is a product of the base volume times a positive-integer
exponentiated ratio of the maximum rate to the nominal rate.
5. The method of claim 2, wherein the base volume is a sum of the
dead volume of the reservoir plus a standard volume, and the
standard volume is a volume of reductant solution in a purchasable
container of reductant solution appropriately matched to the SCR
device.
6. The method of claim 2, wherein maximum rate is substantially
twice the nominal rate.
7. An emissions-control system operatively coupled to an exhaust
system of a vehicle, the emissions-control system comprising: a
reservoir configured to contain a liquid; an SCR device disposed in
the exhaust system; a reductant-delivery system configured to draw
the liquid from the reservoir at a nominal rate and at a maximum
rate, greater than the nominal rate, and further configured to pump
the liquid to the SCR device; a base sensor responsive to whether a
volume of liquid in the reservoir exceeds a base volume greater
than a dead volume of the reservoir; an elevated sensor responsive
to whether the volume of liquid in the reservoir exceeds an
elevated volume, where the elevated volume is a product of the base
volume times a ratio of the maximum rate to the nominal rate; an
emissions sensor responsive to a NOX level in the exhaust-system;
and a misformulation indicator operatively coupled to the emissions
sensor and to at least one of the base sensor and the elevated
sensor, and configured to indicate when an excess NOX emission
follows, within an interval, an increase in the volume of liquid in
the reservoir above at least one of the base volume and the
elevated volume.
8. The emissions-control system of claim 7, wherein the liquid
comprises a reductant solution appropriately matched to the SCR
device.
9. The emissions-control system of claim 7, further comprising an
insufficiency indicator operatively coupled to the base sensor and
configured to indicate when the volume of liquid in the reservoir
falls below the base volume.
10. The emissions-control system of claim 7, where the elevated
sensor is one in a series of elevated sensors corresponding to a
series of elevated volumes, wherein each elevated volume E.sub.i is
given by E.sub.i=B.times.R.sup.i, where B is the base volume, R is
a ratio of the maximum rate to the nominal rate, i is an integer
greater than zero, where each elevated sensor is responsive to
whether the volume of liquid in the reservoir exceeds a
corresponding elevated volume; and where the misformulation
indicator is further configured to indicate when an excess NOX
emission follows, within the interval, an increase in the volume of
liquid in the reservoir above any elevated volume in the series of
elevated volumes.
11. The emissions-control system of claim 7, wherein the base
sensor is responsive to whether a level of liquid in the reservoir
approaches a threshold level to within a tolerance interval, where
the base volume B is related to the threshold level Lo according to
B = .intg. h = 0 L 0 S ( h ) h , ##EQU00002## where S(h) is a
surface area of the liquid in the reservoir when a surface of the
liquid is a height h above a lowest point inside the reservoir.
12. The emissions-control system of claim 11, wherein the tolerance
interval is not symmetric about the threshold level.
13. The emissions-control system of claim 11, wherein the tolerance
interval is chosen such that a response of the base sensor to an
addition of the standard volume of liquid to the reservoir, when
the volume of liquid in the reservoir is initially below the base
volume, occurs statistically at a 3.sigma. level, based on expected
operating conditions of the vehicle.
14. The emissions-control system of claim 7, wherein the elevated
sensor is responsive to whether a level of liquid in the reservoir
approaches a threshold level to within a tolerance interval, where
the elevated volume E.sub.i is related to the threshold level
L.sub.i according to E i = .intg. h = 0 L i S ( h ) h ,
##EQU00003## where S(h) is a surface area of the liquid in the
reservoir when a surface of the liquid is a height h above a lowest
point inside the reservoir.
15. A method to detect at least one of an insufficient reductant
solution and a misformulated reductant solution in vehicle, the
method comprising: containing the reductant solution in a reservoir
equipped with a level-sensing system, comprising: a base sensor
responsive to whether a volume of liquid in the reservoir exceeds a
base volume, where the base volume is a sum of a dead volume of the
reservoir plus a standard volume, and a series of elevated sensors
corresponding to a series of elevated volumes, wherein each
elevated volume is a product of the base volume times a positive
integer power of two, and wherein each elevated sensor is
responsive to whether the volume of liquid in the reservoir exceeds
a corresponding elevated volume; indicating that the reductant
solution is insufficient when the volume of liquid in the reservoir
becomes less than the base volume; and indicating that the
reductant solution is misformulated when an excess NOX emission
follows, within an interval, an increase in the volume of liquid in
the reservoir above any elevated volume in the series of elevated
volumes.
16. The method of claim 15, wherein the excess NOX emission
includes a NOX level failing to respond expectedly to an increasing
rate of withdrawal of reductant solution from the reservoir.
17. The method of claim 15, further comprising initiating a warning
chain when the volume of liquid in the reservoir becomes less than
the base volume.
18. The method of claim 15, further comprising applying other
diagnostics when the excess NOX emission is detected, but does not
follow, within the interval, an increase in the volume of liquid in
the reservoir above any elevated volume in the series of elevated
volumes.
19. The method of claim 15, further indicating that reductant
solution has been added to the reservoir when the volume of liquid
in the reservoir exceeds the base volume.
20. The method of claim 19, further comprising suspending the
warning chain when the volume of liquid in the reservoir exceeds
the base volume.
Description
TECHNICAL FIELD
[0001] The present application relates to the field of emissions
control in vehicles, and more particularly, to control of
nitrogen-oxide emissions from diesel-powered vehicles.
BACKGROUND AND SUMMARY
[0002] An emissions-control system in a vehicle may include a
selective catalytic reduction (SCR device) device, wherein nitrogen
oxide (NOX) emissions from an engine are combined with ammonia to
form dinitrogen and water vapor. Ammonia may be supplied to the
exhaust system of the vehicle via a reductant solution, e.g.
aqueous urea. Maintenance of the quantity and quality of the
reductant solution enables the benefits of the SCR device to be
achieved through the operation of the system.
[0003] Therefore, U.S. Pat. No. 6,363,771 B1 describes a diagnostic
system for a vehicle. The diagnostic system described therein is
configured to detect when a level of the reductant solution in a
reservoir descends below a threshold, and, based on such detection,
to alert the operator of the vehicle when a refill is necessary.
Further, the diagnostic system may be configured to detect when the
solution contained in the reductant reservoir is misformulated,
based on an adverse effect of misformulated reductant solution on
NOX emissions. To determine whether NOX emissions are adversely
affected, the diagnostic system interacts with the
emissions-control system of the vehicle.
[0004] However, the inventors herein have recognized a flaw in this
approach. Specifically, a diagnostic system as described above may
not be able to distinguish a misformulated reductant solution from
other causes of emissions-control error. If the diagnostic system
determines incorrectly that the reductant solution in a vehicle is
misformulated, it may issue erroneous warnings or take
inappropriate corrective action--limiting speed or engine power,
for example--which may be antagonistic to the operator of the
vehicle. Therefore, the inventors herein have provided a way to
test for insufficient or misformulated reductant in an integrated
approach that heuristically distinguishes the misformulated
reductant from other causes of emissions-control error.
[0005] In one embodiment, an example emissions control system of a
vehicle is provided. The emissions-control system is operatively
coupled to an exhaust system of the vehicle; it includes a
reservoir configured to contain a reductant solution, and an SCR
device disposed in the exhaust system and configured to consume the
reductant solution. The example emissions-control system further
includes a base sensor responsive to whether a volume of the
reductant solution exceeds a base volume, wherein the base volume
is a sum of a dead volume of the reservoir plus a standard volume,
and, a series of elevated sensors corresponding to a series of
elevated volumes, wherein each elevated volume is a product of the
base volume times a positive integer power of two, and wherein each
elevated sensor is responsive to whether the volume of the
reductant solution exceeds a corresponding elevated volume. The
example emissions-control system further includes an emissions
sensor responsive to a NOX level in the exhaust system, and a
misformulation indicator operatively coupled to the emissions
sensor and to at least one of the base sensor and any elevated
sensor, and configured to indicate when an excess NOX emission
follows, within an interval, an increase in the volume of the
reductant solution above the base volume or any elevated volume in
the series of elevated volumes. The example emissions-control
system may further include an insufficiency indicator operatively
coupled to the base volume sensor and configured to indicate when
the volume of the reductant solution becomes less than the base
volume.
[0006] Another embodiment provides a method of evaluating a
reductant solution stored on-board a vehicle in a reservoir, the
vehicle having a reductant-delivery system for delivering the
reductant solution to an SCR device in an exhaust system of the
vehicle. This example method includes varying a reductant-solution
delivery rate in response to a reductant-solution concentration to
maintain emissions-control performance, and distinguishing
misformulation of the reductant solution from other
emissions-control system errors based on a volume change in the
reservoir in combination with an emissions-control performance
assay.
[0007] Still other embodiments provide different emissions-control
systems and related methods to detect at least one of an
insufficient reductant solution and a misformulated reductant
solution in vehicle. In addition to numerous other advantages,
these systems and methods may reduce the likelihood that an error
sensed by an emissions-control system in a vehicle will be falsely
attributed to improper maintenance of the reductant solution,
thereby enabling more accurate diagnosis of the cause of the
error.
[0008] It will be understood that the summary above is provided to
introduce in simplified form a selection of concepts that are
further described in the detailed description. It is not meant to
identify key or essential features of the claimed subject matter,
the scope of which is defined by the claims that follow the
detailed description. Further, the claimed subject matter is not
limited to implementations that solve any disadvantages noted above
or in any part of this disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 shows elements of an example emissions-control system
of a vehicle, in accordance with the present disclosure.
[0010] FIG. 2 shows elements of an example emissions-control system
of a vehicle equipped with an example level sensor, in accordance
with the present disclosure.
[0011] FIG. 3 illustrates an example method to provide ammonia to
an SCR device disposed in an exhaust system of a vehicle, in
accordance with the present disclosure.
DETAILED DESCRIPTION
[0012] FIG. 1 shows elements of an emissions-control system of a
vehicle in one, example embodiment. Emissions-control system 100
includes SCR device 102 and reservoir 104. The SCR device is
disposed in an exhaust system of the vehicle; it includes a
catalytically active surface, where nitrogen-based reducing agents
(ammonia, urea, etc.) may react with NOX, forming dinitrogen and
water vapor. The reservoir is configured to contain a liquid, which
is intended to be a reductant solution appropriately matched to the
SCR device. For example, the liquid may be an aqueous urea solution
of a concentration recommended for use with the SCR device. Further
the capacity of the reservoir may be chosen based on a nominal
rate, u.sub.N, of delivery of the reductant solution to the SCR
device, and further based on a desired mileage range of the
vehicle. For example, the capacity of the reservoir may be
sufficient to allow the vehicle to travel the desired mileage
range, while consuming the reductant solution at the nominal rate
of consumption.
[0013] Emissions-control system 100 includes reductant-delivery
system 106, which is configured to draw liquid from reservoir 104
at the nominal rate u.sub.N. As shown in FIG. 1, the liquid drawn
from the reservoir is delivered to SCR device 102.
Reductant-delivery system 106 may include any pump suitable for
delivering an aqueous solution from the reservoir to the SCR
device; it may include a mechanical pump--a centrifugal pump, a
reciprocating pump, etc.--or, in other embodiments, a source of
compressed air or gas configured to pressurize the reservoir and
force the liquid therefrom. In some embodiments, the
reductant-delivery system may be configured to draw liquid from the
reservoir at a plurality of different rates, which include the
nominal rate u.sub.N, rates less than the nominal rate, and rates
greater than the nominal rate. In one embodiment, the
reductant-delivery system may be configured to draw liquid from the
reservoir over a range of rates from zero (no delivery) to a
maximum rate u.sub.M>u.sub.N.
[0014] The volume of liquid contained in reservoir 104 may vary
during operation of the vehicle. Thus, FIG. 1 shows a variable
level L of liquid in the reservoir, below which level a variable
volume V of liquid is contained. FIG. 1 also shows certain fixed
volumes within the reservoir; these include dead volume D and base
volume B. Dead volume D is a volume of liquid that cannot be
reliably withdrawn from the reservoir by reductant-delivery system
106. The dead volume is a consequence of the detailed configuration
of the reservoir and the reductant-delivery system. Although the
reservoir and the reductant-delivery system may be configured to
minimize the dead volume, various design considerations may result
in some dead volume remaining.
[0015] Emissions-control system 100 includes base sensor 108,
insufficiency indicator 110, and controller 112. The base sensor
may be a sensor responsive to whether variable volume V exceeds
base volume B. In one embodiment, the base sensor may an
appropriately configured level sensor, as described hereinafter,
with reference to FIG. 2. The insufficiency indicator may include
various indicators--visual, audible, etc.--configured to indicate
when variable volume V falls below base volume B. To that end, the
insufficiency indicator may be operatively coupled to the base
sensor via the controller. In some embodiments, activation of the
insufficiency indicator may initiate a sequence of derating
conditions in the vehicle intended to limit engine output when
reductant solution for the SCR device becomes unavailable. The
derating conditions may include, for example, vehicle speed
governance, throttle governance, ignition suppression, etc. The
emissions-control system may be configured to reset the
insufficiency indicator when the variable volume V exceeds base
volume B, as reported by the base sensor.
[0016] In some embodiments, base volume B is the sum of dead volume
D plus a standard volume S. The standard volume S may be a fixed
volume; it may be a unit volume or an integer multiple of a unit
volume: one gallon, three liters, etc. In some embodiments, the
standard volume may be the volume of reductant solution provided in
a purchasable container of reductant solution appropriate for use
in the vehicle. The standard volume may be selected in this manner
to ensure that adding the entire contents of one purchasable
container of reductant solution will result in variable volume V
exceeding base volume B. As indicated above, this condition may
trigger a reset of insufficiency indicator 110, and thereby suspend
one or more derating conditions that may be in place.
[0017] Emissions-control system 100 further includes emissions
sensor 114. The emissions sensor may be any sensor responsive to a
NOX level in the exhaust system of the vehicle. The emissions
sensor may be configured to perform an emissions-control assay,
e.g. to detect, infer, or measure NOX level in the exhaust system,
a level of any NOX constituent, parameters indicative of emission
levels, or another condition correlated to exhaust NOX levels. The
emissions sensor may further be configured to sense or detect an
excess NOX level in the exhaust system. In some embodiments,
reductant-delivery system 106 may be operatively coupled to
emissions sensor 114 via controller 112, in a closed-loop manner.
For example, the controller may be configured to vary the rate of
delivery of the reductant solution to SCR device 102 so as to use
as little reductant solution as possible while maintaining the NOX
level below an acceptable limit. In doing so, the controller may
vary the rate of delivery of the reductant solution among a
plurality of delivery rates that the reductant-delivery system is
configured to provide.
[0018] During a course of operation of the vehicle, liquid may be
added to reservoir 104 according to various schedules or scenarios.
Some scenarios include accidental or deliberate misformulation of
the reductant solution by an operator of the vehicle. For example,
some operators may delay adding reductant solution to the reservoir
until insufficiency indicator 110 becomes active and indicates that
a derating condition may follow. The operator of the vehicle, aware
that the derating condition is linked to the volume of liquid in
the reservoir, may add liquid at that time, thereby resetting the
insufficiency indicator and suspending the derating condition.
[0019] Ideally, the liquid that the operator adds to reservoir 104
will be a reductant solution of a composition and concentration
appropriate for the vehicle. But in some cases, an operator may add
a different liquid, resulting in the reductant solution becoming
misformulated; the operator may add reductant solution of an
incorrect composition, a too-dilute reductant solution, or water,
for example.
[0020] Emissions-control system 100 may be configured to tolerate
dilution of an otherwise-correctly formulated reductant solution
within certain limits. For example, controller 112 may be
configured to increase the rate of delivery of reductant solution
to SCR device 102 when the nominal rate of delivery fails to
maintain the NOX level below an acceptable limit. In one
embodiment, reductant-delivery system 106 may be configured to draw
the liquid from the reservoir at a nominal rate u.sub.N and at a
maximum rate u.sub.M, greater than the nominal rate. The controller
may be configured to switch the rate of delivery of reductant
solution from the nominal rate to the maximum rate as needed to
maintain the NOX level below the acceptable limit. In other
embodiments, reductant-delivery system 106 may be configured to
draw the liquid from the reservoir over a range of rates from
substantially zero to the maximum rate u.sub.M. Such embodiments
may admit of a threshold concentration of reductant solution below
which the NOX level cannot be kept below the acceptable limit. For
example, a threshold concentration C.sub.M may be related to the
nominal rate u.sub.N and to the maximum rate u.sub.M by
C.sub.Nu.sub.N=C.sub.Mu.sub.M, where C.sub.N is a nominal
concentration of reductant solution intended for use in the
vehicle.
[0021] When the reductant solution is further diluted, such that
the concentration falls below C.sub.M, an emissions-control error
may result. For example, emissions sensor 114 may indicate that a
NOX level is above an acceptable limit, although reductant-delivery
system 106 is delivering liquid to the SCR device at the maximum
rate u.sub.M. Therefore, emissions-control system 100 further
includes misformulation indicator 116, which is operatively coupled
to emissions sensor 114 via controller 112 and configured to
indicate that the reductant solution in reservoir 104 is
misformulated. However, as the NOX level may exceed the acceptable
limit due to various other malfunctions unrelated to the reductant
solution, emissions-control system 100 may be further configured to
apply a heuristic to assess whether the emissions-control error is
likely caused by a misformulation of the reductant solution or
whether some other fault is indicated. In one example, the
operation described herein enables such a heuristic using a
straightforward and inexpensive configuration--one that comprises a
few discrete level sensors, as opposed to more costly alternatives.
Nevertheless, the approach described herein may be combined with
such other approaches without departing from the scope of this
disclosure.
[0022] The following illustrates one example heuristic for
assessing a cause of emissions-control error according to the
example configuration described herein.
[0023] An emissions-control error may occur when insufficiency
indicator 110 is inactive, e.g., when variable volume V exceeds the
base volume B. Let t.sub.B be the time since the variable volume V
last traversed the base volume, and let .tau. be the time required
to substantially deplete and refill the ammonia atmosphere in SCR
device 102 under current vehicle operating conditions. If
t.sub.B<.tau., it may be considered likely that the
emissions-control error is due to a misformulation of the reductant
solution that occurred during the most recent addition of liquid to
reservoir 104. However, if t.sub.B>.tau., it may be considered
likely that the emissions-control error is unrelated to the most
recent addition of liquid to the reservoir.
[0024] The above example shows how a time of traversal of the
variable volume V above the base volume B may figure into a
heuristic for assessing whether misformulation of the reductant
solution is a likely cause of emissions-control error. It is
possible, however, that misformulation of the reductant solution
may occur and may cause an emissions-control error when the
variable volume does not traverse the base volume. To enable
assessment under such conditions, emissions-control system 100
further includes elevated sensor 118A, which may be a sensor
responsive to whether the variable volume V exceeds elevated volume
E.sub.1. In one embodiment, the elevated sensor may an
appropriately configured level sensor, as described hereinafter,
with reference to FIG. 2. As shown in FIG. 1, elevated volume
E.sub.1 may be the product B.times.R, where R=u.sub.M/u.sub.N.
[0025] Suppose that the variable volume V is between the base
volume B and the elevated volume E.sub.1, that the NOX level is
below the acceptable limit, and that reductant-delivery system 106
is supplying the reductant solution at the nominal rate u.sub.N. It
will be observed that dilution of the reductant solution to a
volume less than E.sub.1 will yield a concentration greater than
the threshold concentration C.sub.M. It should be possible, under
such conditions, to avoid an emissions-control error by delivering
the reductant solution to SCR device 102 at an accelerated rate, as
described above. However, if the reductant solution is diluted such
that the final volume exceeds E.sub.1, it is then possible that the
concentration of the reductant solution may fall below C.sub.M,
triggering an emissions-control error.
[0026] The example heuristic may now be extended as follows. An
emissions-control error may occur, as before, when insufficiency
indicator 110 is inactive. Let t.sub.E be the time since the
variable volume V last traversed elevated volume E.sub.1. If
t.sub.E<.tau., it may be considered likely that the
emissions-control error is due to a misformulation of the reductant
solution that occurred during the most recent addition of liquid to
reservoir 104. However, if t.sub.E>.tau., it may be considered
likely that the emissions-control error is unrelated to the most
addition of liquid to the reservoir.
[0027] Thus, at a heuristic level, assessment of whether an
emissions-control error is due to misformulation of the reductant
solution may be based on whether at least one of a base volume and
an elevated volume have been exceeded in an interval preceding the
emissions-control error, wherein the interval corresponds to the
time required to substantially empty and refill the ammonia
atmosphere in SCR device 102. Therefore, in one embodiment, the
misformulation indicator may be operatively coupled to emissions
sensor 114, to base sensor 108 and to elevated sensor 118A. The
misformulation indicator may be configured to indicate when an
excess NOX emission follows, within the interval, an increase in
variable volume V above at least one of base volume B and elevated
volume E.sub.1.
[0028] As illustrated in FIG. 1, elevated sensor 118A may be one in
a series of elevated sensors (i.e., 118A, 118B, 118C, etc.)
corresponding to a series of elevated volumes, wherein each
elevated volume E.sub.i is given by E.sub.i=B.times.R.sup.i, and
wherein each elevated sensor is responsive to whether the variable
volume V exceeds a corresponding elevated volume E.sub.i. Further,
in embodiments that comprise a series of elevated sensors,
misformulation indicator 116 may be further configured to indicate
when an excess NOX emission follows, within the interval described
above, an increase in variable volume V above any elevated volume
E.sub.i in the series of elevated volumes.
[0029] The functionality of emissions-control system 100 is most
easily understood with reference to a non-limiting, example
embodiment in which the maximum delivery rate u.sub.M is
substantially twice that of the nominal delivery rate u.sub.N,
i.e., R.apprxeq.2. In this embodiment, the series of elevated
volumes comprise a geometric series, E.sub.1=2B, E.sub.2=4B,
E.sub.3=8B, etc.
[0030] It will be understood that emissions-control systems fully
consistent with this disclosure may include various other
components not shown in FIG. 1: lean NOX traps, diesel oxidation
catalyst modules, diesel particulate filters, as examples.
[0031] In some embodiments, one or more of base sensor 108 and
elevated sensors 118A, 118B, etc. may include a level sensor.
Therefore, FIG. 2 shows, in schematic detail, an example level
sensor 200. As described hereinafter, a level sensor may be
configured to sense whether a variable volume V of liquid in a
reservoir traverses a fixed volume (e.g., the base volume or an
elevated volume). It will be understood, however, that some
embodiments fully consistent with this disclosure may employ an
approach other than level sensing to sense whether a volume of
liquid in a reservoir traverses a fixed volume.
[0032] Continuing in FIG. 2, level sensor 200 includes
level-sensing element 202, which is held in place by support
structure 204. The level-sensing element may be any
element-electronic, optical, acoustic, etc.--responsive to whether
a variable level L of liquid approaches a threshold level L.sub.0
to within a tolerance interval, which may be any interval that
brackets the threshold level L.sub.0. For example, the tolerance
interval may be the interval
L.sub.0-.alpha..ltoreq.L.ltoreq.L.sub.0+.beta., where the
parameters .alpha. and .beta. may or may not be equal (vide
infra).
[0033] As shown in FIG. 2, level-sensing element 202 is operatively
coupled to controller 112; thus, the controller may be configured
to provide a bias to the level-sensing element as well as register
a response therefrom. In some embodiments, the level-sensing
element may give a steady response whenever the variable level is
within the tolerance interval, while in other embodiments, the
level-sensing element may respond transiently to variable level L
passing into or out of the tolerance interval. Further, the
level-sensing element may be configured to respond differently
depending on whether the variable level passes into the tolerance
interval from above or whether it passes into the tolerance
interval from below. Such functionality may be due to a
configuration of the level sensing element, the controller, or
both.
[0034] In the illustrated embodiment, level-sensing element 202 may
respond to variable level L approaching threshold level L.sub.0
because it is disposed substantially at the threshold level, is
immersed in liquid when the variable level is above the tolerance
interval, and is not immersed in liquid when the variable level is
below the tolerance interval. In such embodiments, support
structure 204 fixes the vertical position of the level-sensing
element and thereby fixes the threshold level L.sub.0 relative to
the lowest point in reservoir 104. In FIG. 2, the support structure
couples the level sensing element to an inside surface of the
reservoir. It will be understood, however, that various other
embodiments are contemplated, including those in which the support
structure extends downward from the top of the reservoir, thereby
suspending the level sensing element a fixed vertical distance from
the top of the reservoir. In still other embodiments, the level
sensing element may be responsive to the liquid level even if it is
not immersed in the liquid (e.g., if it is disposed outside the
reservoir).
[0035] In embodiments that employ a level sensor, such as level
sensor 200, to determine whether a variable volume exceeds a fixed
volume, the fixed volume V.sub.0 and the threshold level L.sub.0
may be related according to
V 0 = .intg. h = 0 L 0 S ( h ) h , ##EQU00001##
where S(h) is a surface area of the liquid in the reservoir when a
surface of the liquid is a height h above a lowest point inside the
reservoir.
[0036] In one particular embodiment, wherein base sensor 108
includes level sensor 200, the fixed volume V.sub.0 in the equation
above may correspond to base volume B, and the tolerance interval
may be disposed so that 0.ltoreq..beta.<.alpha.. An asymmetric
tolerance interval such as this may chosen so that a response of
the base sensor to an addition of the standard volume of liquid to
the reservoir, when the volume of liquid in the reservoir is
initially below the base volume, occurs statistically at a 3.sigma.
level, based on expected operating conditions of the vehicle.
[0037] FIG. 3 illustrates an example method to detect at least one
of an insufficient reductant solution and a misformulated reductant
solution in a vehicle, in a manner consistent with the example
configurations set forth above.
[0038] Method 300 begins at 302, where a reductant solution is
contained within a reservoir. As noted above, the reservoir may be
equipped with a level-sensing system. The level-sensing system may
include a base sensor responsive to whether a volume of liquid in
the reservoir exceeds a base volume B, where the base volume is a
sum of a dead volume of the reservoir plus a standard volume. The
level-sensing system may further include a series of elevated
sensors corresponding to a series of elevated volumes E.sub.i,
wherein each elevated volume is the base volume times a positive
integer power of two, and wherein each elevated sensor is
responsive to whether the volume of liquid in the reservoir exceeds
a corresponding elevated volume.
[0039] Method 300 continues to 304, where it is determined whether
a variable volume V of liquid in the reservoir exceeds the base
volume B. If the variable volume does not exceed the base volume,
then, at 306, insufficiency of the reductant solution is indicated.
Insufficiency of the reductant solution may be indicated via an
insufficiency indicator, substantially as described above. The
indication of reductant-solution insufficiency may trigger, at 308,
a warning chain; it may further trigger a derating sequence
intended to limit emissions from the vehicle. It will be understood
that `warning chain,` as used herein, may comprise any inducement
or series of inducements intended to encourage the operator of the
vehicle to maintain the quantity and/or quality of the reductant
solution. The warning chain may be responsive at least partly to a
distance that the vehicle travels after reductant-solution
insufficiency is indicated, e.g., from an output of a vehicle
odometer or other distance-responsive vehicle component. In other
embodiments fully consistent with this disclosure, the warning
chain may be responsive at least partly to a number of engine
revolutions or other suitable surrogate. In one particular
embodiment, the warning chain may be based on an average rate of
consumption of reductant solution (in milliliters per mile, for
example) and on the estimated volume of reductant solution
remaining in the reservoir, based on distance travelled after
reductant-solution insufficiency is indicated. Thus, the average
rate of consumption may be used to calculate various threshold
distances used in the warning chain.
[0040] Continuing in method 300, if it is determined at 304 that
the variable volume exceeds the base volume, then, at 310, any
pre-existing insufficiency indication is cleared, and any
associated warning chain and/or derating sequence is suspended.
This step may further include indicating that reductant solution
has been added to the reservoir.
[0041] Method 300 then continues to 312, where it is determined
whether a NOX level in the exhaust system is below an acceptable
limit. This determination may be pursuant to an emissions-control
assay, which may be enabled by an emissions sensor disposed in an
exhaust system of the vehicle, as described hereinabove. In some
embodiments, this determination may include assessing whether the
NOX level does or does not respond expectedly to an increasing rate
of delivery of reductant solution to an SCR device of the vehicle.
If the NOX level is below the acceptable limit, then execution
resumes at 304. However, if it is determined that the NOX level
exceeds the acceptable limit, then, at 314, it is determined
whether the excess NOX emission has followed, within an interval,
an increase in the volume of liquid in the reservoir above either
the base volume or any elevated volume in the series of elevated
volumes. In one embodiment, the interval selected for this purpose
may include a time to deplete and refill a nominal operating amount
of ammonia in the SCR device of the vehicle. If it is determined
that the excess NOX emission has followed such an increase in
volume within the interval, then, at 316, misformulation of the
reductant solution is indicated. Misformulation of the reductant
solution may be indicated via a misformulation indicator,
substantially as described hereinabove.
[0042] However, if it is determined at 314 that the excess NOX
emission did not follow, within the interval, an increase in the
volume of liquid in the reservoir above either the base volume or
any elevated volume in the series of elevated volumes, then, at
320, other warnings and/or diagnostics may be applied to assess the
cause of the excess NOX emission. Then, from 316 or 320, the method
returns to 304.
[0043] It will be understood that the example control and
estimation routines disclosed herein may be used with various
system configurations. These routines may represent one or more
different processing strategies such as event-driven,
interrupt-driven, multi-tasking, multi-threading, and the like. As
such, the disclosed process steps (operations, functions, and/or
acts) may represent code to be programmed into computer readable
storage medium in a control system. It will be understood that some
of the process steps described and/or illustrated herein may in
some embodiments be omitted without departing from the scope of
this disclosure. Likewise, the indicated sequence of the process
steps may not always be required to achieve the intended results,
but is provided for ease of illustration and description. One or
more of the illustrated actions, functions, or operations may be
performed repeatedly, depending on the particular strategy being
used.
[0044] Finally, it will be understood that the systems and methods
described herein are exemplary in nature, and that these specific
embodiments or examples are not to be considered in a limiting
sense, because numerous variations are contemplated. Accordingly,
the present disclosure includes all novel and non-obvious
combinations and sub-combinations of the various systems and
methods disclosed herein, as well as any and all equivalents
thereof.
* * * * *