U.S. patent application number 12/844985 was filed with the patent office on 2012-02-02 for detection of exhaust particulate filter substrate failure.
This patent application is currently assigned to GM GLOBAL TECHNOLOGY OPERATIONS, INC.. Invention is credited to Eugene V. Gonze, Zhiping Steven Liu.
Application Number | 20120023911 12/844985 |
Document ID | / |
Family ID | 45525300 |
Filed Date | 2012-02-02 |
United States Patent
Application |
20120023911 |
Kind Code |
A1 |
Liu; Zhiping Steven ; et
al. |
February 2, 2012 |
DETECTION OF EXHAUST PARTICULATE FILTER SUBSTRATE FAILURE
Abstract
A method of detecting failure of a substrate in a particulate
filter includes comparing an absolute value of a difference between
a theoretical temperature difference and an actual temperature
difference between an upstream end and a downstream end of the
particulate filter to a temperature differential threshold, and
comparing an absolute value of a difference between a theoretical
pressure difference and an actual pressure difference between the
upstream end and the downstream end of the particulate filter to a
pressure differential threshold. Failure of the substrate is
indicated by one or both of the temperature difference and the
pressure difference being greater than the temperature differential
threshold and the pressure differential threshold respectively.
Inventors: |
Liu; Zhiping Steven;
(Canton, MI) ; Gonze; Eugene V.; (Pinckney,
MI) |
Assignee: |
GM GLOBAL TECHNOLOGY OPERATIONS,
INC.
Detroit
MI
|
Family ID: |
45525300 |
Appl. No.: |
12/844985 |
Filed: |
July 28, 2010 |
Current U.S.
Class: |
60/277 |
Current CPC
Class: |
F01N 3/035 20130101;
F01N 3/2066 20130101; F01N 2900/0601 20130101; Y02A 50/20 20180101;
Y02A 50/2325 20180101; F01N 2900/1406 20130101; Y02T 10/47
20130101; Y02T 10/40 20130101; F01N 2560/14 20130101; F01N 2560/08
20130101; F01N 2900/1602 20130101; F01N 2900/1606 20130101; F01N
11/005 20130101; F01N 2550/04 20130101; F01N 11/002 20130101 |
Class at
Publication: |
60/277 |
International
Class: |
F01N 11/00 20060101
F01N011/00 |
Claims
1. A method of detecting a failure in a substrate of a particulate
filter in an exhaust system of a vehicle, the method comprising:
calculating an absolute value of a difference between a theoretical
temperature difference between an upstream end and a downstream end
of the particulate filter and an actual temperature difference
between the upstream end and the downstream end of the particulate
filter; comparing the absolute value of the difference between the
theoretical temperature difference and the actual temperature
difference to a temperature differential threshold to determine if
the absolute value of the difference between the theoretical
temperature difference and the actual temperature difference is
greater than the temperature differential threshold; calculating an
absolute value of a difference between a theoretical pressure
difference between the upstream end and the downstream end of the
particulate filter and an actual pressure difference between the
upstream end and the downstream end of the particulate filter;
comparing the absolute value of the difference between the
theoretical pressure difference and the actual pressure difference
to a pressure differential threshold to determine if the absolute
value of the difference between the theoretical pressure difference
and the actual pressure difference is greater than the pressure
differential threshold; and indicating a substrate failure if the
absolute value of the difference between the theoretical
temperature difference and the actual temperature difference is
greater than the temperature differential threshold or if the
absolute value of the difference between the theoretical pressure
difference and the actual pressure difference is greater than the
pressure differential threshold.
2. A method as set forth in claim 1 further comprising defining a
particulate matter threshold.
3. A method as set forth in claim 2 further comprising detecting a
particulate matter level of particulate matter trapped in the
particulate filter.
4. A method as set forth in claim 3 further comprising comparing
the particulate matter level to the particulate matter threshold to
determine if the particulate matter level is greater than the
particulate matter threshold.
5. A method as set forth in claim 4 wherein comparing the
particulate matter level to the particulate matter threshold is
further defined as comparing the particulate matter level to the
particulate matter threshold after comparing the absolute value of
the difference between the theoretical temperature difference and
the actual temperature difference to the temperature differential
threshold.
6. A method as set forth in claim 5 wherein comparing the
particulate matter level to the particulate matter threshold is
further defined as comparing the particulate matter level to the
particulate matter threshold before comparing the absolute value of
the difference between the theoretical pressure difference and the
actual pressure difference to the pressure differential
threshold.
7. A method as set forth in claim 6 further comprising stopping
analysis of the substrate without indicating a substrate failure
prior to comparing the absolute value of the difference between the
theoretical pressure difference and the actual pressure difference
to the pressure differential threshold when the particulate matter
level is greater than the particulate matter threshold.
8. A method as set forth in claim 1 further comprising defining the
theoretical temperature difference between the upstream end and the
downstream end of the particulate filter.
9. A method as set forth in claim 8 wherein defining the
theoretical temperature difference includes calculating a
theoretical upstream temperature and a theoretical downstream
temperature of the exhaust gas for the current operating conditions
of the exhaust system.
10. A method as set forth in claim 8 wherein defining the
theoretical temperature difference includes referencing stored
temperature values from a table for the current operating
conditions of the exhaust system to determine a theoretical
upstream temperature and a theoretical downstream temperature of
the exhaust gas.
11. A method as set forth in claim 1 further comprising defining
the theoretical pressure difference between the upstream end and
the downstream end of the particulate filter.
12. A method as set forth in claim 11 wherein defining the
theoretical pressure difference includes calculating a theoretical
upstream pressure and a theoretical downstream pressure of the
exhaust gas for the current operating conditions of the exhaust
system.
13. A method as set forth in claim 11 wherein defining the
theoretical pressure difference includes referencing stored
pressure values from a table for the current operating conditions
of the exhaust system to determine a theoretical upstream pressure
and a theoretical downstream pressure of the exhaust gas.
14. A method as set forth in claim 1 further comprising measuring
the actual temperature difference between the upstream end and the
downstream end of the particulate filter.
15. A method as set forth in claim 1 further comprising measuring
the actual pressure difference between the upstream end and the
downstream end of the particulate filter.
16. A method as set forth in claim 1 further comprising defining
the temperature differential threshold.
17. A method as set forth in claim 1 further comprising defining
the pressure differential threshold.
18. A method as set forth in claim 1 further comprising stopping
analysis of the substrate without indicating a substrate failure if
the absolute value of the difference between the theoretical
temperature difference and the actual temperature difference is
less than the temperature differential threshold and if the
absolute value of the difference between the theoretical pressure
difference and the actual pressure difference is less than the
pressure differential threshold.
19. A method of detecting a failure in a substrate of a particulate
filter in an exhaust system of a vehicle, the method comprising:
measuring the actual temperature difference between an upstream end
and a downstream end of the particulate filter; calculating an
absolute value of a difference between a theoretical temperature
difference between the upstream end and the downstream end of the
particulate filter and the actual temperature difference between
the upstream end and the downstream end of the particulate filter;
comparing the absolute value of the difference between the
theoretical temperature difference and the actual temperature
difference to a temperature differential threshold to determine if
the absolute value of the difference between the theoretical
temperature difference and the actual temperature difference is
greater than the temperature differential threshold; comparing a
measured particulate matter level of particulate matter trapped in
the particulate filter to a particulate matter threshold to
determine if the particulate matter level is greater than the
particulate matter threshold; measuring the actual pressure
difference between the upstream end and the downstream end of the
particulate filter; calculating an absolute value of a difference
between a theoretical pressure difference between the upstream end
and the downstream end of the particulate filter and an actual
pressure difference between the upstream end and the downstream end
of the particulate filter; comparing the absolute value of the
difference between the theoretical pressure difference and the
actual pressure difference to a pressure differential threshold to
determine if the absolute value of the difference between the
theoretical pressure difference and the actual pressure difference
is greater than the pressure differential threshold when the
particulate matter level is less than the particulate matter
threshold; and indicating a substrate failure if the absolute value
of the difference between the theoretical temperature difference
and the actual temperature difference is greater than the
temperature differential threshold, or if the absolute value of the
difference between the theoretical pressure difference and the
actual pressure difference is greater than the pressure
differential threshold.
20. A method as set forth in claim 19 wherein comparing a
particulate matter level of particulate matter trapped in the
particulate filter to a particulate matter threshold is further
defined as comparing the particulate matter level to the
particulate matter threshold after comparing the absolute value of
the difference between the theoretical temperature difference and
the actual temperature difference to the temperature differential
threshold.
Description
TECHNICAL FIELD
[0001] The invention generally relates to a method of detecting
failure of a substrate in a particulate filter of an exhaust system
of a vehicle.
BACKGROUND
[0002] An exhaust system for a vehicle may include a particulate
filter. If the engine includes a diesel engine, then the
particulate filter is commonly referred to as a diesel particulate
filter. The particulate filter filters particulate matter, i.e.,
soot, from the exhaust gas of the engine. The particulate filter
may include one or more substrates that define a plurality of
apertures, through which the exhaust gas must flow. The particulate
matter collects on the substrate as the exhaust gas flows through
the apertures. The particulate filter is occasionally regenerated
to remove the collected particulate matter. Regeneration of the
particulate filter includes heating the particulate filter to a
temperature sufficient to burn the collected particulate matter,
which converts the particulate matter to carbon dioxide that
dissipates into the atmosphere.
[0003] An on board diagnostic system may monitor the status of the
particulate filter to determine if the particulate filter, and
specifically the substrate, has failed. Failure of the substrate
may include, but is not limited to, damage to the substrate or
removal of the substrate.
SUMMARY
[0004] A method of detecting a failure in a substrate of a
particulate filter in an exhaust system of a vehicle is provided.
The method includes calculating an absolute value of a difference
between a theoretical temperature difference between an upstream
end and a downstream end of the particulate filter, and an actual
temperature difference between the upstream end and the downstream
end of the particulate filter, and comparing the absolute value of
the difference between the theoretical temperature difference and
the actual temperature difference to a temperature differential
threshold to determine if the absolute value of the difference
between the theoretical temperature difference and the actual
temperature difference is greater than the temperature differential
threshold. The method further includes calculating an absolute
value of a difference between a theoretical pressure difference
between the upstream end and the downstream end of the particulate
filter and an actual pressure difference between the upstream end
and the downstream end of the particulate filter, and comparing the
absolute value of the difference between the theoretical pressure
difference and the actual pressure difference to a pressure
differential threshold to determine if the absolute value of the
difference between the theoretical pressure difference and the
actual pressure difference is greater than the pressure
differential threshold. The method further includes indicating a
substrate failure if the absolute value of the difference between
the theoretical temperature difference and the actual temperature
difference is greater than the temperature differential threshold,
or if the absolute value of the difference between the theoretical
pressure difference and the actual pressure difference is greater
than the pressure differential threshold.
[0005] A method of detecting a failure in a substrate of a
particulate filter in an exhaust system of a vehicle is also
provided. The method includes measuring the actual temperature
difference between an upstream end and a downstream end of the
particulate filter, calculating an absolute value of a difference
between a theoretical temperature difference between the upstream
end and the downstream end of the particulate filter and the actual
temperature difference between the upstream end and the downstream
end of the particulate filter, and comparing the absolute value of
the difference between the theoretical temperature difference and
the actual temperature difference to a temperature differential
threshold to determine if the absolute value of the difference
between the theoretical temperature difference and the actual
temperature difference is greater than the temperature differential
threshold. The method further includes comparing a measured
particulate matter level of particulate matter trapped in the
particulate filter to a particulate matter threshold to determine
if the particulate matter level is greater than the particulate
matter threshold. The method further includes measuring the actual
pressure difference between the upstream end and the downstream end
of the particulate filter, calculating an absolute value of a
difference between a theoretical pressure difference between the
upstream end and the downstream end of the particulate filter and
an actual pressure difference between the upstream end and the
downstream end of the particulate filter, and comparing the
absolute value of the difference between the theoretical pressure
difference and the actual pressure difference to a pressure
differential threshold to determine if the absolute value of the
difference between the theoretical pressure difference and the
actual pressure difference is greater than the pressure
differential threshold when the particulate matter level is less
than the particulate matter threshold. The method further includes
indicating a substrate failure if the absolute value of the
difference between the theoretical temperature difference and the
actual temperature difference is greater than the temperature
differential threshold, or if the absolute value of the difference
between the theoretical pressure difference and the actual pressure
difference is greater than the pressure differential threshold.
[0006] Accordingly, both the temperature differential and the
pressure differential between the upstream end and the downstream
end of the particulate filter are examined to detect a failure of
the substrate in the particulate filter. A thermal mass of the
particulate filter causes the temperature downstream of the
particulate filter to be less than a temperature upstream of the
particulate filter. During normal operation of the particulate
filter, the temperature differential between the upstream end and
the downstream end of the particulate filter falls below a
temperature differential threshold. Damage too or removal of the
substrate causes the temperature differential between the upstream
end and the downstream end of the particulate filter to rise above
the temperature differential threshold. Similarly, a flow
restriction in the particulate filter causes a pressure downstream
of the particulate filter to be less than a pressure upstream of
the particulate filter. During normal operation of the particulate
filter, the pressure differential between the upstream end and the
downstream end of the particulate filter falls below a pressure
differential threshold. Damage to or removal of the substrate
causes the pressure differential between the upstream end and the
downstream end of the particulate filter to rise above the pressure
differential threshold. Accordingly, comparing the actual
temperature differential and the actual pressure differential the
temperature differential threshold and the pressure differential
threshold respectively may indicate damage too or removal of the
substrate. Using both the temperature and the pressure of the
particulate increases the ability to detect damage and/or removal
of the substrate.
[0007] The above features and advantages and other features and
advantages of the present invention are readily apparent from the
following detailed description of the best modes for carrying out
the invention when taken in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a schematic diagram of an engine and an exhaust
system of a vehicle.
[0009] FIG. 2 is a flow chart showing a method of detecting failure
in a substrate of a particulate filter of the exhaust system.
DETAILED DESCRIPTION
[0010] Referring to FIG. 1, wherein like numerals indicate like
parts throughout the several views, an exhaust system is generally
shown at 20. The exhaust system 20 is coupled to an engine 22 of a
vehicle. The engine 22 may include, but is not limited to, a diesel
engine 22. Fuel ignites within a plurality of cylinders (not shown)
of the engine 22, producing a flow of exhaust gas that is directed
through the exhaust system 20 in a direction indicated by arrow 23.
The exhaust system 20 treats the exhaust gas to reduce undesirable
emissions, and remove particulate matter, i.e., soot, from the
exhaust gas.
[0011] The exhaust system 20 may include an oxidation catalyst 24.
The oxidation catalyst 24 includes a flow-through honeycomb
structure that is covered with a chemical catalyst. The chemical
catalyst may include a precious metal, including but not limited
to, platinum or palladium. The chemical catalyst, when heated to a
light-off temperature, interacts with and oxidizes pollutants in
the exhaust gas, such as carbon monoxide and unburned hydrocarbons,
thereby reducing undesirable emissions. The oxidation catalyst 24
may include any suitable type of oxidation catalyst 24, and may be
sized and or configured in any suitable manner required to meet
specific design parameters.
[0012] The exhaust system 20 may further include a Selective
Catalytic Reduction (SCR) system 26. The SCR system 26 includes an
exhaust fluid injector 28, which injects an exhaust fluid, such as
but not limited to a mixture of urea and water, into the flow of
exhaust gas. A mixer 30 mixes the exhaust fluid with the exhaust
gas. When heated by the exhaust gas, the exhaust fluid forms
ammonia. The SCR system 26 further includes a converter 32. The
converter 32 includes a catalyst that causes or accelerates a
chemical reaction between the ammonia created by the exhaust fluid
and the NOx (nitrogen oxides) in the exhaust gas to form nitrogen
and water vapor.
[0013] The exhaust system 20 further includes a particulate filter
34. The particulate filter 34 filters particulate matter, i.e.,
soot, from the exhaust gas of the engine 22. The particulate filter
34 may include one or more substrate 36 that define a plurality of
apertures, through which the exhaust gas must flow. The particulate
matter collects on the substrate 36 as the exhaust gas flows
through the apertures. The particulate filter 34 is occasionally
regenerated to remove the collected particulate matter.
Regeneration of the particulate filter 34 includes heating the
particulate filter 34 to a temperature sufficient to burn the
collected particulate matter to carbon dioxide.
[0014] As shown, the particulate filter 34 is disposed downstream
of the converter 32. The particulate filter 34 includes an upstream
end 38, disposed between the converter 32 and the particulate
filter 34, and a downstream end 40, disposed opposite the upstream
end 38 of the particulate filter 34.
[0015] The exhaust system 20 further includes a first temperature
sensor 42 and a second temperature sensor 44. The first temperature
sensor 42 is disposed adjacent the upstream end 38 of the
particulate filter 34, and the second temperature sensor 44 is
disposed adjacent the downstream end 40 of the particulate filter
34. The first temperature sensor 42 measures a temperature of the
exhaust gas upstream of the particulate filter 34. The second
temperature sensor 44 measures a temperature of the exhaust gas
downstream of the particulate filter 34. The first temperature
sensor 42 and the second temperature sensor 44 may include any
suitable temperature sensor capable of sensing the temperature of
the exhaust gas within the exhaust system 20. Because the
particulate filter 34 includes a thermal mass, the particulate
filter 34 absorbs heat from the exhaust gas as the exhaust gas
flows through the particulate filter 34. Accordingly, during normal
operation, the temperature of the exhaust gas at the second
temperature sensor 44 is less than the temperature of the exhaust
gas at the first temperature sensor 42. When the particulate filter
34, and particularly the substrate 36 of the particulate filter 34,
is operating properly, a temperature differential between the first
temperature sensor 42 and the second temperature sensor 44 falls
within a given temperature range for given operating conditions.
Accordingly, if the temperature differential is outside the given
temperature range for a specific operating condition, and
particularly greater than an upper temperature threshold, then it
is likely that the thermal mass of the particulate filter 34 has
been altered. For example, removal and/or damage of the substrate
36 may cause the temperature differential between the first
temperature sensor 42 and the second temperature to fall outside
the given temperature range.
[0016] The exhaust system 20 further includes a first pressure
sensor 46 and a second pressure sensor 48. The first pressure
sensor 46 is disposed adjacent the upstream end 38 of the
particulate filter 34, and the second pressure sensor 48 is
disposed adjacent the downstream end 40 of the particulate filter
34 The first pressure sensor 46 measures a fluid pressure, i.e.,
gas pressure, of the exhaust gas upstream of the particulate filter
34. The second pressure sensor 48 measures a fluid pressure, i.e.,
gas pressure, of the exhaust gas downstream of the particulate
filter 34. The first pressure sensor 46 and the second pressure
sensor 48 may include any suitable pressure sensor capable of
sensing the fluid pressure of the exhaust gas within the exhaust
system 20.
[0017] Because the particulate filter 34 redirects the flow of
exhaust gas through the apertures of the substrate 36, the
particulate filter 34 decreases the fluid pressure, i.e., the gas
pressure, as the exhaust gas flows through the particulate filter
34. Accordingly, during normal operation, the pressure of the
exhaust gas at the second pressure sensor 48 is less than the
pressure of the exhaust gas at the first pressure sensor 46. When
the particulate filter 34, and particularly the substrate 36 of the
particulate filter 34, is operating properly, a pressure
differential between the first pressure sensor 46 and the second
pressure sensor 48 falls within a given pressure range for given
operating conditions. Accordingly, if the pressure differential is
outside the given pressure range for a specific operating
condition, and particularly greater than an upper pressure
threshold, then it is likely that the flow path of the exhaust gas
through the particulate filter 34 has been altered. For example,
removal and/or damage of the substrate 36 may cause the pressure
differential between the first pressure sensor 46 and the second
pressure sensor 48 to fall outside the given pressure range.
[0018] Referring to FIG. 2, a method of detecting a failure in the
substrate 36 of the particulate filter 34 in the exhaust system 20
of the vehicle is shown generally at 50. The method includes
defining a theoretical temperature difference between the upstream
end 38 and the downstream end 40 of the particulate filter 34,
block 52. The theoretical temperature difference is the temperature
difference between the first temperature sensor 42 and the second
temperature sensor 44 that should occur if the particulate filter
34 and particularly the substrate 36 are operating properly.
[0019] Defining the theoretical temperature difference may include
calculating a theoretical upstream temperature and a theoretical
downstream temperature of the exhaust gas for the current operating
conditions of the exhaust system 20. The theoretical downstream
temperature is subtracted from the theoretical upstream temperature
to obtain the theoretical temperature difference. For example, an
equation may be generated to calculate the theoretical upstream
temperature and the theoretical downstream temperature based on the
mass of the exhaust gas, the flow rate of the exhaust gas,
temperature of the exhaust gas upstream of the particulate filter
34, the time over which the theoretical temperature difference is
calculated, or some other known variable of the exhaust system
20.
[0020] Alternatively, defining the theoretical temperature
difference may include referencing stored temperature values from a
table of temperature values for the current operating conditions of
the exhaust system 20 to determine the theoretical upstream
temperature and the theoretical downstream temperature of the
exhaust gas. The theoretical downstream temperature is subtracted
from the theoretical upstream temperature to obtain the theoretical
temperature difference. The theoretical upstream temperature and
the theoretical downstream temperature for specific operating
conditions may be determined, for example, through testing at
various operating conditions. These values may be stored in memory
of an engine control unit, and may be referenced to determine the
theoretical upstream temperature and the theoretical downstream
temperature of the exhaust gas for the current operating conditions
of the engine 22 and the exhaust system 20. Accordingly, the engine
control unit may learn the current operating conditions of the
engine 22 and the exhaust system 20, and use the current operating
conditions to reference the temperature table to determine the
theoretical upstream temperature and the theoretical downstream
temperature of the exhaust gas.
[0021] The method further includes measuring the actual temperature
difference between the upstream end 38 and the downstream end 40 of
the particulate filter 34, block 54. The first temperature sensor
42 measures an actual upstream temperature of the exhaust gas, and
the second temperature sensor measures an actual downstream
temperature of the exhaust gas. The actual downstream temperature
is subtracted from the actual upstream temperature to obtain the
actual temperature difference between the upstream end 38 and the
downstream end 40 of the particulate filter 34.
[0022] The method further includes calculating an absolute value of
the difference between the theoretical temperature difference
between the upstream end 38 and the downstream end 40 of the
particulate filter 34, and the actual temperature difference
between the upstream end 38 and the downstream end 40 of the
particulate filter 34, block 56. The absolute value is the real
number value of the difference, regardless of a positive or
negative sign. Accordingly, the actual temperature difference is
subtracted from the theoretical temperature difference to obtain
the temperature difference between the theoretical temperature
difference and the actual temperature difference. The absolute
value is then taken of the temperature difference between the
theoretical temperature difference and the actual temperature
difference.
[0023] The method further includes defining a temperature
differential threshold, block 58. The temperature differential
threshold is an upper temperature limit associated with proper
operation of the particulate filter 34 and/or the substrate 36.
Accordingly, a temperature below the temperature differential
threshold is indicative of proper functioning of the particulate
filter 34 and/or the substrate 36, whereas a temperature above the
temperature differential threshold is indicative of a failure of
the particulate filter 34 and/or the substrate 36.
[0024] The method further includes comparing the absolute value of
the difference between the theoretical temperature difference and
the actual temperature difference to the temperature differential
threshold, block 60. The absolute value of the temperature
difference is compared to the temperature differential threshold to
determine if the absolute value of the difference between the
theoretical temperature difference and the actual temperature
difference is greater than the temperature differential
threshold.
[0025] If the absolute value of the temperature difference between
the theoretical temperature difference and the actual temperature
difference is greater than the temperature differential threshold,
indicated at 62, then the method further includes indicating a
substrate 36 failure, block 64. The failure may be indicated in any
suitable manner, including but not limited to displaying a warning
light and/or sound, or otherwise scheduling maintenance.
[0026] If the absolute value of the temperature difference is less
than the temperature differential threshold, indicated at 66, then
the method further includes defining a particulate matter
threshold, block 68. The particulate matter threshold is the
maximum recommended amount of particulate matter deposited or
trapped within the particulate filter 34. An amount of particulate
matter above the particulate matter threshold may adversely affect
the flow of the exhaust gas through the particulate filter 34.
[0027] The method further includes detecting a particulate matter
level of particulate matter trapped in the particulate filter 34,
block 70, and comparing the particulate matter level to the
particulate matter threshold to determine if the particulate matter
level is greater than the particulate matter threshold, block 72.
The particulate matter level is the current level or amount of
particulate matter deposited or trapped within the particulate
filter 34. The particulate matter level may be determined in any
suitable manner, including but not limited to the use of sensors
and/or calculations. The particulate matter level may be compared
to the particulate matter threshold after comparing the absolute
value of the temperature difference to the temperature differential
threshold.
[0028] If the particulate matter level is less than the particulate
matter threshold, indicated at 74, then the method further includes
defining a theoretical pressure difference between the upstream end
38 and the downstream end 40 of the particulate filter 34, block
76. The theoretical pressure difference is the pressure difference
between the first pressure sensor and the second pressure sensor 48
that should occur if the particulate filter 34 and particularly the
substrate 36 are operating properly.
[0029] Defining the theoretical pressure difference may include
calculating a theoretical upstream pressure and a theoretical
downstream pressure of the exhaust gas for the current operating
conditions of the exhaust system 20. The theoretical downstream
pressure is subtracted from the theoretical upstream pressure to
obtain the theoretical pressure difference. For example, an
equation may be generated to calculate the theoretical upstream
pressure and the theoretical downstream pressure based on the flow
rate of the exhaust gas, the temperature of the exhaust gas
upstream of the particulate filter 34, or some other known variable
of the exhaust system 20.
[0030] Alternatively, defining the theoretical pressure difference
may include referencing stored pressure values from a table of
pressure values for the current operating conditions of the exhaust
system 20 to determine the theoretical upstream pressure and the
theoretical downstream pressure of the exhaust gas. The theoretical
downstream pressure is subtracted from the theoretical upstream
pressure to obtain the theoretical pressure difference. The
theoretical upstream pressure and the theoretical downstream
pressure for specific operating conditions may be determined, for
example, through testing at various operating conditions. These
values may be stored in memory of the engine control unit, and may
be referenced to determine the theoretical upstream pressure and
the theoretical downstream pressure of the exhaust gas for the
current operating conditions of the engine 22 and the exhaust
system 20. Accordingly, the engine control unit may learn the
current operating conditions of the engine 22 and the exhaust
system 20, and use the current operating conditions to reference
the pressure table to determine the theoretical upstream
temperature and the theoretical downstream temperature of the
exhaust gas.
[0031] The method further includes measuring the actual pressure
difference between the upstream end 38 and the downstream end 40 of
the particulate filter 34, block 78. The first pressure sensor 46
measures an actual upstream pressure of the exhaust gas, and the
second pressure sensor 48 measures an actual downstream pressure of
the exhaust gas. The actual downstream pressure is subtracted from
the actual upstream pressure to obtain the actual pressure
difference between the upstream end 38 and the downstream end 40 of
the particulate filter 34.
[0032] The method further includes calculating an absolute value of
the difference between the theoretical pressure difference between
the upstream end 38 and the downstream end 40 of the particulate
filter 34, and the actual pressure difference between the upstream
end 38 and the downstream end 40 of the particulate filter 34,
block 80. The absolute value is the real number value of the
difference, regardless of a positive or negative sign. Accordingly,
the actual pressure difference is subtracted from the theoretical
pressure difference to obtain the pressure difference between the
theoretical pressure difference and the actual pressure difference.
The absolute value is then taken of the pressure difference between
the theoretical pressure difference and the actual pressure
difference.
[0033] The method further includes defining a pressure differential
threshold, block 82. The pressure differential threshold is an
upper pressure limit associated with proper operation of the
particulate filter 34 and/or the substrate 36. Accordingly, a
pressure below the pressure differential threshold is indicative of
proper functioning of the particulate filter 34 and/or the
substrate 36, whereas a pressure above the pressure differential
threshold is indicative of a failure of the particulate filter 34
and/or the substrate 36.
[0034] The method further includes comparing the absolute value of
the difference between the theoretical pressure difference and the
actual pressure difference to the pressure differential threshold,
block 84. The absolute value of the pressure difference is compared
to determine if the absolute value of the difference between the
theoretical pressure difference and the actual pressure difference
is greater than the pressure differential threshold.
[0035] If the absolute value of the difference between the
theoretical pressure difference and the actual pressure difference
is greater than the pressure differential threshold, indicated at
86, then the method may further include indicating a substrate 36
failure, block 64. The failure may be indicated in any suitable
manner, including but not limited to displaying a warning light
and/or sound, or otherwise scheduling maintenance.
[0036] If the absolute value of the difference between the
theoretical temperature difference and the actual temperature
difference is less than the temperature differential threshold,
indicated at 66, and if the absolute value of the difference
between the theoretical pressure difference and the actual pressure
difference is less than the pressure differential threshold,
indicated at 88, then the method may further include stopping
analysis of the substrate 36 without indicating a substrate 36
failure, block 90.
[0037] If the particulate matter level is greater than the
particulate matter threshold, indicated at 92, then the method may
further include stopping analysis of the substrate 36 without
indicating a substrate 36 failure, block 90. The analysis is exited
prior to comparing the absolute value of the difference between the
theoretical pressure difference and the actual pressure difference
to the pressure differential threshold, block 84. If the
particulate matter level is greater than the particulate matter
threshold, indicated at 92, then the elevated particulate matter
level may adversely affect the upstream pressure and/or downstream
pressure of the exhaust gas, rendering the analysis between the
theoretical pressure difference and the actual pressure difference
inaccurate. Specifically, the elevated particulate matter level
increases fluid flow resistance through the particulate filter 34,
thereby increasing the upstream pressure and/or decreasing the
downstream pressure. As such, the pressure analysis to determine if
the substrate 36 has failed may be abandoned because the altered
actual pressure difference may render the analysis untrustworthy.
Therefore, it should be appreciated that the particulate matter
level is compared to the particulate matter threshold before
comparing the absolute value of the difference between the
theoretical pressure difference and the actual pressure difference
to the pressure differential threshold.
[0038] While the best modes for carrying out the invention have
been described in detail, those familiar with the art to which this
invention relates will recognize various alternative designs and
embodiments for practicing the invention within the scope of the
appended claims.
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